Compositions and methods for drug delivery using pH sensitive molecules

ABSTRACT

A system relating to the delivery of desired compounds (e.g., drugs and nucleic acids) into cells using pH-sensitive delivery systems. The system provides compositions and methods for the delivery and release of a compound to a cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of prior provisionalapplications 60/137,859 filed on Jun. 7, 1999, 60/167,836 filed on Nov.29, 1999 and 60/172,809 filed on Dec. 21, 1999.

FIELD OF THE INVENTION

[0002] The present invention relates to the delivery of desiredcompounds (e.g., drugs and nucleic acids) into cells using pH-sensitivedelivery systems. The present invention provides compositions andmethods for the delivery and release of a compound of interest to acell.

BACKGROUND OF THE INVENTION

[0003] Drug Delivery

[0004] A variety of methods and routes of administration have beendeveloped to deliver pharmaceuticals that include small molecular drugsand biologically active compounds such as peptides, hormones, proteins,and enzymes to their site of action. Parenteral routes of administrationinclude intravascular (intravenous, intraarterial), intramuscular,intraparenchymal, intradermal, subdermal, subcutaneous, intratumor,intraperitoneal, and intralymphatic injections that use a syringe and aneedle or catheter. The blood circulatory system provides systemicspread of the pharmaceutical. Polyethylene glycol and other hydrophilicpolymers have provided protection of the pharmaceutical in the bloodstream by preventing its interaction with blood components and toincrease the circulatory time of the pharmaceutical by preventingopsonization, phagocytosis and uptake by the reticuloendothelial system.For example, the enzyme adenosine deaminase has been covalently modifiedwith polyethylene glycol to increase the circulatory time andpersistence of this enzyme in the treatment of patients with adenosinedeaminase deficiency.

[0005] The controlled release of pharmaceuticals after theiradministration is under intensive development. Pharmaceuticals have alsobeen complexed with a variety of biologically-labile polymers to delaytheir release from depots. These polymers have included copolymers ofpoly(lactic/glycolic acid) (PLGA) (Jain, R. et al. Drug Dev. Ind. Pharm.24, 703-727 (1998), ethylvinyl acetate/polyvinyl alcohol (Metrikin, D Cand Anand, R, Curr Opin Ophthalmol 5, 21-29, 1994) as typical examplesof biodegradable and non-degradable sustained release systemsrespectively.

[0006] Transdermal routes of administration have been effected bypatches and ionotophoresis. Other epithelial routes include oral, nasal,respiratory, and vaginal routes of administration. These routes haveattracted particular interest for the delivery of peptides, proteins,hormones, and cytokines, which are typically administered by parenteralroutes using needles. For example, the delivery of insulin viarespiratory, oral, or nasal routes would be very attractive for patientswith diabetes mellitus. For oral routes, the acidity of the stomach (pHless than 2) is avoided for pH-sensitive compounds by concealingpeptidase-sensitive polypaptides inside pH-sensitive hydrogel matrix(copolymers of polyethyleneglycol and polyacrylic acid). After passinglow pH compartments of gastrointestinal tract such structures swells athigher pH releasing thus a bioactive compound (Lowman A M et al. J.Pharm. Sci. 88, 933-937 (1999). Capsules have also been developed thatrelease their contents within the small intestine based uponpH-dependent solubility of a polymer. Copolymers of polymethacrylic acid(Eudragit S, Rohm America) are known as polymers which are insoluble atlower pH but readily solubilized at higher pH, so they are used asenteric coatings (Z Hu et al. J. Drug Target., 7, 223, 1999).

[0007] Biologically active molecules may be assisted by a reversibleformation of covalent bonds. Quite often, it is found that the drugadministered to a patient is not the active form of the drug, but iswhat is a called a prodrug that changes into the actual biologicallyactive compound upon interactions with specific enzymes inside the body.In particular, anticancer drugs are quite toxic and are administered asprodrugs which do not become active until they come in contact with thecancerous cell (Sezaki, I I., Takakura, Y., Hashida, M. Adv. Drug.Delivery Reviews 3, 193, 1989).

[0008] Recent studies have found that pH in solid tumors is 0.5 to 1units lower than in normal tissue (Gerweck L E et al. Cancer Res. 56,1194 (1996). Hence, the use of pH-sensitive polymers for tumor targetingis justified. However, this approach was demonstrated only in vitro(Berton, M, Eur. J. Pharm. Biopharm. 47, 119-23, 1999).

[0009] Liposomes were also used as drug delivery vehicles for lowmolecular weight drugs and macromolecules such as amphotericin B forsystemic fungal infections and candidiasis. Inclusion of anti-cancerdrugs such as adriamycin have been developed to increase their deliveryto tumors and reduce it to other tissue sites (e.g. heart) therebydecreasing their toxicity. pH-sensitive polymers have been used inconjunction with liposomes for the triggered release of an encapsulateddrug. For example, hydrophobically-modifiedN-isopropylacrylamide-methacrylic acid copolymer can render regular eggphosphatidyl chloline liposomes pH-sensitive by pH-dependent interactionof grafted aliphatic chains with lipid bilayer (O Meyer et al., FEBSLett., 421, 61, 1998).

[0010] Gene and Nucleic Acid-Based Delivery

[0011] Gene or polynucleotide transfer is the cardinal process of genetherapy. The gene needs to be transferred across the cell membrane andenter the nucleus where the gene can be expressed. Gene transfer methodscurrently being explored included viral vectors and physical-chemicalmethods.

[0012] Viruses have evolved over millions of year to transfer theirgenes into mammalian cells. Viruses can be modified to carry a desiredgene and become a “vector” for gene therapy. Using standard recombinanttechniques, the harmful or superfluous viral genes can be removed andreplaced with the desired normal gene. This was first accomplished withmouse retroviruses. The development of retroviral vectors were thecatalyst that promoted current gene therapy efforts. However, theycannot infect all cell types very efficiently, especially in vivo. Otherviral vectors based on Herpes virus are being developed to enable moreefficient gene transfer into brain cells. Adenoviral and adenoassociatedvectors are being developed to infect lung and other cells.

[0013] Besides using viral vectors, it is possible to directly transfergenes into mammalian cells. Usually, the desired gene is placed withinbacterial plasmid DNA along with a mammalian promoter, enhancer, andother sequences that enable the gene to be expressed in mammalian cells.Several milligrams of the plasmid DNA containing all these sequences canbe prepared and purified from the bacterial cultures. The plasmid DNAcontaining the desired gene can be incorporated into lipid vesicles(liposomes including cationic lipids such as Lipofectin) that thentransfer the plasmid DNA into the target cell. Plasmid DNA can also becomplexed with proteins that target the plasmid DNA to specific tissuesjust as certain proteins are taken up (endocytosed) by specific cells.Also, plasmid DNA can be complexed with polymers such as polylysine andpolyethylenimine. Another plasmid-based technique involves “shooting”the plasmid DNA on small gold beads into the cell using a “gun”.Finally, muscle cells in vivo have the unusual ability to take up andexpress plasmid DNA.

[0014] Gene therapy approaches can be classified into direct andindirect methods. Some of these gene transfer methods are most effectivewhen directly injected into a tissue space. Direct methods using many ofthe above gene transfer techniques are being used to target tumors,muscle, liver, lung, and brain. Other methods are most effective whenapplied to cells or tissues that have been removed from the body and thegenetically-modified cells are then transplanted back into the body.Indirect approaches in conjunction with retroviral vectors are beingdeveloped to transfer genes into bone marrow cells, lymphocytes,hepatocytes, myoblasts and skin cells.

[0015] Gene Therapy and Nucleic Acid-Based Therapies

[0016] Gene therapy promises to be a revolutionary advance in thetreatment of disease. It is a fundamentally new approach for treatingdisease that is different from the conventional surgical andpharmaceutical therapies. Conceptually, gene therapy is a relativelysimple approach. If someone has a defective gene, then gene therapywould fix the defective gene. The disease state would be modified bymanipulating genes instead of their products, i.e. proteins, enzymes,enzyme substrates and enzyme products. Although, the initial motivationfor gene therapy was the treatment of genetic disorders, it is becomingincreasingly apparent that gene therapy will be useful for the treatmentof a broad range of acquired diseases such as cancer, infectiousdisorders (AIDS), heart disease, arthritis, and neurodegenerativedisorders (Parkinson's and Alzheimer's).

[0017] Gene therapy promises to take full-advantage of the majoradvances brought about by molecular biology. While, biochemistry ismainly concerned with how the cell obtains the energy and matter that isrequired for normal function, molecular biology is mainly concerned withhow the cell gets the information to perform its functions. Molecularbiology wants to discover the flow of information in the cell. Using themetaphor of computers, the cell is the hardware while the genes are thesoftware. In this sense, the purpose of gene therapy is to provide thecell with a new program (genetic information) so as to reprogram adysfunctional cell to perform a normal function. The addition of a newcellular function is provided by the insertion of a foreign gene thatexpresses a foreign protein or a native protein at amounts that are notpresent in the patient.

[0018] The inhibition of a cellular function is provided by anti-senseapproaches (that is acting against messenger RNA) and that includesoligonucleotides complementary to the messenger RNA sequence andribozymes. Messenger RNA (mRNA) is an intermediate in the expression ofthe DNA gene. The mRNA is translated into a protein. “Anti-sense”methods use a RNA sequence or an oligonucleotide that is madecomplementary to the target mRNA sequence and therefore bindsspecifically to the target messenger RNA. When this anti-sense sequencebinds to the target mRNA, the mRNA is somehow destroyed or blocked frombeing translated. Ribozymes destroy a specific mRNA by a differentmechanism. Ribozymes are RNA's that contain sequence complementary tothe target messenger RNA plus a RNA sequence that acts as an enzyme tocleave the messenger RNA, thus destroying it and preventing it frombeing translated. When these anti-sense or ribozyme sequences areintroduced into a cell, they would inactivate their specific target mRNAand reduce their disease-causing properties.

[0019] Several recessive genetic disorders are being considered for genetherapy. One of the first uses of gene therapy in humans has been usedfor the genetic deficiency of the adenosine deaminase (ADA) gene. Otherclinical gene therapy trials have been conducted for cystic fibrosis,familial hypercholesteremia caused by a defective LDL-receptor gene andpartial ornithine transcarbomylase deficiency. Both indirect and directgene therapy approaches are being developed for Duchenne musculardystrophy. Patients with this type of muscular dystrophy eventually diefrom loss of their respiratory muscles. Direct approaches include theintramuscular injection of naked plasmid DNA or adenoviral vectors.

[0020] A wide variety of gene therapy approaches for cancer are underinvestigation in animals and in human clinical trials. One approach isto express in lymphocytes and in the tumor cells, cytokine genes thatstimulate the immune system to destroy the cancer cells. The cytokinegenes would be transferred into the lymphocytes by removing thelymphocytes from the body and infecting them with a retroviral vectorcarrying the cytokine gene. The tumor cells would be similarlygenetically modified by this indirect approach to express cytokineswithin the tumor. Direct approaches involving the expression ofcytokines in tumor cells in situ are also being considered. Other genesbesides cytokines may be able to induce an immune response against thecancer. One approach that has entered clinical trials is the directinjection of HLA-B7 gene (which encodes a potent immunogen) within lipidvesicles into malignant melanomas in order to induce a more effectiveimmune response against the cancer.

[0021] “Suicide” genes are genes that kill cells that express the gene.For example, the diphtheria toxin gene directly kills cells. The Herpesthymidine kinase (TK) gene kills cells in conjunction with acyclovir (adrug used to treat Herpes viral infections). Other gene therapyapproaches take advantage of our knowledge of oncogenes and suppressortumor genes—also known as anti-oncogenes. The loss of a functioninganti-oncogene plays a decisive role in childhood tumors such asretinoblastoma, osteosarcoma and Wilms tumor and may play an importantrole in more common tumors such as lung, colon and breast cancer.Introduction of the normal anti-oncogene back into these tumor cells mayconvert them back to normal cells. The activation of oncogenes alsoplays an important role in the development of cancers. Since theseoncogenes operate in a “dominant” fashion, treatment will requireinactivation of the abnormal oncogene. This can be done using either“anti-sense” or ribozyme methods that selectively inactivate a specificmessenger RNA in a cell.

[0022] Gene therapy can be used as a type of vaccination to preventinfectious diseases and cancer. When a foreign gene is transferred intoa cell and the protein is made, the foreign protein is presented to theimmune system differently from simply injecting the foreign protein intothe body. This different presentation is more likely to cause acell-mediated immune response which is important for fighting latentviral infections such as human immunodeficiency virus (HIV causes AIDS),Herpes and cytomegalovirus. Expression of the viral gene within a cellsimulates a viral infection and induces a more effective immune responseby fooling the body that the cell is actually infected by the virus,without the danger of an actual viral infection.

[0023] One direct approach uses the direct intramuscular injection ofnaked plasmid DNA to express a viral gene in muscle cells. The “gun” hasalso been shown to be effective at inducing an immune response byexpressing foreign genes in the skin. Other direct approaches involvingthe use of retroviral, vaccinia or adenoviral vectors are also beingdeveloped. An indirect approach has been developed to remove fibroblastsfrom the skin, infect them with a retroviral vector carrying a viralgene and transplant the cells back into the body. The envelope gene fromthe AIDS virus (HIV) is often used for these purposes. Many cancer cellsexpress specific genes that normal cells do not. Therefore, these genesspecifically expressed in cancer cells can be used for immunizationagainst cancer.

[0024] Besides the above immunization approaches, several other genetherapies are being developed for treating infectious disease. Most ofthese new approaches are being developed for HIV infection and AIDS.Many of them will involve the delivery of anti-sense or ribozymesequences directed against the particular viral messenger RNA. Theseanti-sense or ribozyme sequences will block the expression of specificviral genes and abort the viral infection without damaging the infectedcell. Another approach somewhat similar to the ant-sense approaches isto overexpress the target sequences for these regulatory HIV sequences.

[0025] Gene therapy efforts would be directed at lowering the riskfactors associated with atherosclerosis. Overexpression of the LDLreceptor gene would lower blood cholesterol in patients not only withfamilial hypercholesteremia but with other causes of high cholesterollevels. The genes encoding the proteins for HDL (“the good cholesterol”)could be expressed also in various tissues. This would raise HDL levelsand prevent atherosclerosis and heart attacks. Tissue plasminogenactivator (tPA) protein is being given to patients immediately aftertheir myocardial infarction to digest the blood clots and open up theblocked coronary blood vessels. The gene for tPA could be expressed inthe endothelial cells lining the coronary blood vessels and therebydeliver the tPA locally without providing tPA throughout the body.Another approach for coronary vessel disease is to express a gene in theheart that produces a protein that causes new blood vessels to grow.This would increase collateral blood flow and prevent a myocardialinfarction from occurring.

[0026] Neurodegenerative disorders such as Parkinson's and Alzheimer'sdiseases are good candidates for early attempts at gene therapy.Arthritis could also be treated by gene therapy. Several proteins andtheir genes (such as the IL-1 receptor antagonist protein) have recentlybeen discovered to be anti-inflammatory. Expression of these genes injoint (synovial) fluid would decrease the joint inflammation and treatthe arthritis.

[0027] In addition, methods are being developed to directly modify thesequence of target genes and chromosomal DNA. The delivery of a nucleicacid or other compound that modifies the genetic instruction (e.g., byhomologous recombination) can correct a mutated gene or mutate afunctioning gene.

[0028] Polymers for Drug and Nucleic Acid Delivery

[0029] Polymers are used for drug delivery for a variety of therapeuticpurposes. Polymers have also been used in research for the delivery ofnucleic acids (polynucleotides and oligonucleotides) to cells with aneventual goal of providing therapeutic processes. Such processes havebeen termed gene therapy or anti-sense therapy. One of the severalmethods of nucleic acid delivery to the cells is the use ofDNA-polycation complexes. It has been shown that cationic proteins likehistones and protamines or synthetic polymers like polylysine,polyarginine, polyornithine, DEAE dextran, polybrene, andpolyethylenimine may be effective intracellular delivery agents whilesmall polycations like spermine are ineffective. The following are someimportant principles involving the mechanism by which polycationsfacilitate uptake of DNA:

[0030] Polycations provide attachment of DNA to the cell surface. Thepolymer forms a cross-bridge between the polyanionic nucleic acids andthe polyanionic surfaces of the cells. As a result the main mechanism ofDNA translocation to the intracellular space might be non-specificadsorptive endocytosis which may be more effective then liquidendocytosis or receptor-mediated endocytosis. Furthermore, polycationsare a convenient linker for attaching specific ligands to DNA and asresult, DNA-polycation complexes can be targeted to specific cell types.

[0031] Polycations protect DNA in complexes against nucleasedegradation. This is important for both extra—and intracellularpreservation of DNA. Gene expression is also enabled or increased bypreventing endosome acidification with NH₄Cl or chloroquine.Polyethylenimine, which facilitates gene expression without additionaltreatments, probably disrupts endosomal function itself. Disruption ofendosomal function has also been accomplished by linking to thepolycation endosomal-disruptive agents such as fusion peptides oradenoviruses.

[0032] Polycations can also facilitate DNA condensation. The volumewhich one DNA molecule occupies in a complex with polycations isdrastically lower than the volume of a free DNA molecule. The size of aDNA/polymer complex is probably critical for gene delivery in vivo. Interms of intravenous injection, DNA needs to cross the endothelialbarrier and reach the parenchymal cells of interest. The largestendothelia fenestrae (holes in the endothelial barrier) occur in theliver and have an average diameter of 100 nm. The trans-epithelial poresin other organs are much smaller, for example, muscle endothelium can bedescribed as a structure which has a large number of small pores with aradius of 4 nm, and a very low number of large pores with a radius of20-30 nm. The size of the DNA complexes is also important for thecellular uptake process. After binding to the cells the DNA-polycationcomplex should be taken up by endocytosis. Since the endocytic vesicleshave a homogenous internal diameter of about 100 nm in hepatocytes andare of similar size in other cell types, DNA complexes smaller than 100nm are preferred.

[0033] Condensation of DNA

[0034] A significant number of multivalent cations with widely differentmolecular structures have been shown to induce condensation of DNA.

[0035] Two approaches for compacting (used herein as an equivalent tothe term condensing) DNA:

[0036] 1. Multivalent cations with a charge of three or higher have beenshown to condense DNA. These include spermidine, spermine, Co(NH₃)₆³⁺,Fe³⁺, and natural or synthetic polymers such as histone H1,protamine, polylysine, and polyethylenimine. Analysis has shown DNAcondensation to be favored when 90% or more of the charges along thesugar-phosphate backbone are neutralized.

[0037] 2. Polymers (neutral or anionic) which can increase repulsionbetween DNA and its surroundings have been shown to compact DNA. Mostsignificantly, spontaneous DNA self-assembly and aggregation processhave been shown to result from the confinement of large amounts of DNA,due to excluded volume effect.

[0038] Depending upon the concentration of DNA, condensation leads tothree main types of structures:

[0039] 1) In extremely dilute solution (about 1 μg/mL or below), longDNA molecules can undergo a monomolecular collapse and form structuresdescribed as toroid.

[0040] 2) In very dilute solution (about 10 μg/mL) microaggregates formwith short or long molecules and remain in suspension. Toroids, rods andsmall aggregates can be seen in such solution.

[0041] 3) In dilute solution (about 1 mg/mL) large aggregates are formedthat sediment readily.

[0042] Toroids have been considered an attractive form for gene deliverybecause they have the smallest size. While the size of DNA toroidsproduced within single preparations has been shown to vary considerably,toroid size is unaffected by the length of DNA being condensed. DNAmolecules from 400 bp to genomic length produce toroids similar in size.Therefore one toroid can include from one to several DNA molecules. Thekinetics of DNA collapse by polycations that resulted in toroids is veryslow. For example DNA condensation by Co(NH₃)₆Cl₃ needs 2 hours at roomtemperature.

[0043] The mechanism of DNA condensation is not clear. The electrostaticforce between unperturbed helices arises primarily from a counterionfluctuation mechanism requiring multivalent cations and plays a majorrole in DNA condensation. The hydration forces predominate overelectrostatic forces when the DNA helices approach closer then a fewwater diameters. In a case of DNA-polymeric polycation interactions, DNAcondensation is a more complicated process than the case of lowmolecular weight polycations. Different polycationic proteins cangenerate toroid and rod formation with different size DNA at a ratio ofpositive to negative charge of two to five. T4 DNA complexes withpolyarginine or histone can form two types of structures; an elongatedstructure with a long axis length of about 350 nm (like free DNA) anddense spherical particles. Both forms exist simultaneously in the samesolution. The reason for the co-existence of the two forms can beexplained as an uneven distribution of the polycation chains among theDNA molecules. The uneven distribution generates two thermodynamicallyfavorable conformations.

[0044] The electrophoretic mobility of DNA-polycation complexes canchange from negative to positive in excess of polycation. It is likelythat large polycations don't completely align along DNA but form polymerloops that interact with other DNA molecules. The rapid aggregation andstrong intermolecular forces between different DNA molecules may preventthe slow adjustment between helices needed to form tightly packedorderly particles.

[0045] As previously stated, preparation of polycation-condensed DNAparticles is of particular importance for gene therapy, morespecifically, particle delivery such as the design of non-viral genetransfer vectors. Optimal transfection activity in vitro and in vivo canrequire an excess of polycation molecules. However, the presence of alarge excess of polycations may be toxic to cells and tissues. Moreover,the non-specific binding of cationic particles to all cells forestallscellular targeting. Positive charge also has an adverse influence onbiodistribution of the complexes in vivo.

[0046] Several modifications of DNA-cation particles have been createdto circumvent the nonspecific interactions of the DNA-cation particleand the toxicity of cationic particles. Examples of these modificationsinclude attachment of steric stabilizers, e.g. polyethylene glycol,which inhibit nonspecific interactions between the cation and biologicalpolyanions. Another example is recharging the DNA particle by theadditions of polyanions which interact with the cationic particle,thereby lowering its surface charge, i.e. recharging of the DNA particleU.S. Pat. No. 09/328,975. Another example is cross-linking the polymersand thereby caging the complex U.S. Pat. No. 08/778,657, U.S. Pat. No.09/000,692, U.S. Pat. No. 97/24089, U.S. Pat. No. 09/070299, and U.S.Pat. No. 09/464,871. Nucleic acid particles can be formed by theformation of chemical bonds and template polymerization U.S. Pat. No.08/778,657, U.S. Pat. No. 09/000,692, U.S. Pat. No. 97/24089, U.S. Pat.No. 09/070299, and U.S. Pat. No. 09/464,871.

[0047] A problem with these modifications is that they are most likelyirreversible rendering the particle unable to interact with the cell tobe transfected, and/or incapable of escaping from the lysosome oncetaken into a cell, and/or incapable of entering the nucleus once insidethe cell. A method for formation of DNA particles that is reversibleunder conditions found in the cell may allow for effective delivery ofDNA. The conditions that cause the reversal of particle formation maybe, but not limited to, the pH, ionic strength, oxidative or reductiveconditions or agents, or enzymatic activity.

[0048] DNA Template Polymerization

[0049] Low molecular weight cations with valency, i.e. charge, <+3 failto condense DNA in aqueous solutions under normal conditions. However,cationic molecules with the charge <+3 can be polymerized in thepresence of DNA and the resulting polymers can cause DNA to condenseinto compact structures. Such an approach is known in synthetic polymerchemistry as template polymerization. During this process, monomers(which are initially weakly associated with the template) are positionedalong template's backbone, thereby promoting their polymerization. Weakelectrostatic association of the nascent polymer and the templatebecomes stronger with chain growth of the polymer. Trubetskoy et al usedtwo types of polymerization reactions to achieve DNA condensation: steppolymerization and chain polymerization (V S Trubetskoy, V G Budker, L JHanson, P M Slattum, J A Wolff, L E Hagstrom. Nucleic Acids Res.26:4178-4185, 1998) U.S. Pat. No. 08/778,657, U.S. Pat. No. 09/000,692,U.S. Pat. No. 97/24089, U.S. Pat. No. 09/070299, and U.S. Pat. No.09/464,871. Bis(2-aminoethyl)-1,3-propanediamine (AEPD), a tetraminewith 2.5 positive charges per molecule at pH 8 was polymerized in thepresence of plasmid DNA using cleavable disulfide amino-reactivecross-linkers dithiobis (succinimidyl propionate) anddimethyl-3,3′-dithiobispropionimidate. Both reactions yieldedDNA/polymer complexes with significant retardation in agaroseelectrophoresis gels demonstrating significant binding and DNAcondensation. Treatment of the polymerized complexes with 100 mMdithiothreitol (DTT) resulted in the pDNA returning to its normalsupercoiled position following electrophoresis proving thus cleavage thebackbone of the. The template dependent polymerization process was alsotested using a 14 mer peptide encoding the nuclear localizing signal(NLS) of SV40 T antigen (SEQ ID NO: 1) as a cationic “macromonomer”.Other studies included pegylated comonomer (PEG-AEPD) into the reactionmixture and resulted in “worm”-like structures (as judged bytransmission electron microscopy) that have previously been observedwith DNA complexes formed from block co-polymers of polylysine and PEG(M A Wolfert, E H Schacht, V Toncheva, K Ulbrich, O Nazarova, L WSeymour. Human Gene Ther. 7:2123-2133, 1996). Blessing et al usedbisthiol derivative of spermine and reaction of thiol-disulfide exchangeto promote chain growth. The presence of DNA accelerated thepolymerization reaction as measured the rate of disappearance of freethiols in the reaction mixture (T Blessing, J S Remy, J P Behr. J. Am.Chem. Soc. 120:8519-8520, 1998).

[0050] “Caging” of Polycation-Condensed DNA Particles.

[0051] The stability of DNA nanoassemblies based on DNA condensation isgenerally low in vivo because they easily engage in polyion exchangereactions with strong polyanions. The process of exchange consists oftwo stages: 1) rapid formation of a triple DNA-polycation-polyanioncomplex, 2) slow substitution of one same-charge polyion with another.At equilibrium conditions, the whole process eventually results information of a new binary complex and an excess of a third polyion. Thepresence of low molecular weight salt can greatly accelerate suchexchange reactions, which often result in complete disassembly ofcondensed DNA particles. Hence, it is desirable to obtain morecolloidally stable structures where DNA would stay in its condensed formin complex with corresponding polycation independently of environmentconditions.

[0052] The complete DNA condensation upon neutralization of only 90% ofthe polymer's phosphates results in the presence of unpaired positivecharges in the DNA particles. If the polycation contains such reactivegroups, such as primary amines, these unpaired positive charges may bemodified. This modification allows practically limitless possibilitiesof modulating colloidal properties of DNA particles via chemicalmodifications of the complex. We have demonstrated the utility of suchreactions using traditional DNA-poly-L-lysine (DNA/PLL) system reactedwith the cleavable cross-linking reagentdimethyl-3,3′-dithiobispropionimidate (DTBP) which reacts with primaryamino groups with formation of amidines (V S Trubetskoy, A Loomis, P MSlattum, J E Hagstrom, V G Budker, J A Wolff. Bioconjugate Chem.10:624-628, 1999) U.S. Pat. No. 08/778,657, U.S. Pat. No. 09/000,692,U.S. Pat. No. 97/24089, U.S. Pat. No. 09/070299, and U.S. Pat. No.09/464,871. Similar results were achieved with other polycationsincluding poly(allylamine) and histone H1. The use of anotherbifucntional reagent, glutaraldehyde, has been described forstabilization of DNA complexes with cationic peptide CWK18 (R C Adam, KG Rice. J. Pharm. Sci. 739-746, 1999).

[0053] Recharging.

[0054] The caging approach described above could lead to morecolloidally stable DNA assemblies. However, this approach may not changethe particle surface charge. Caging with bifunctional reagents, whichpreserve positive charge of amino group, keeps the particle positive.However, negative surface charge would be more desirable for manypractical applications, i.e. in vivo delivery. The phenomenon of surfacerecharging is well known in colloid chemistry and is described in greatdetail for lyophobic/lyophilic systems (for example, silver halidehydrosols). Addition of polyion to a suspension of latex particles withoppositely-charged surface leads to the permanent absorption of thispolyion on the surface and, upon reaching appropriate stoichiometry,changing the surface charge to opposite one. This whole process is saltdependent with flocculation to occur upon reaching the neutralizationpoint.

[0055] We have demonstrated that similar layering of polyelectrolytescan be achieved on the surface of DNA/polycation particles (V STrubetskoy, A Loomis, J E Hagstrom, V G Budker, J A Wolff. Nucleic AcidsRes. 27:3090-3095, 1999). The principal DNA-polycation (DNA/pC) complexused in this study was DNA/PLL (1:3 charge ratio) formed in low salt 25mM HEPES buffer and recharged with increasing amounts of variouspolyanions. The DNA particles were characterized after addition of athird polyion component to a DNA/polycation complex using a new DNAcondensation assay (V S Trubetskoy, P M Slattum, J E Hagstrom, J AWolff, V G Budker. Anal. Biochem. 267:309-313, 1999) and static lightscattering. It has been found that certain polyanions such aspoly(methacrylic acid) and poly(aspartic acid) decondensed DNA inDNA/PLL complexes. Surprisingly, polyanions of lower charge density suchas succinylated PLL and poly(glutamic acid), even when added in 20-foldcharge excess to condensing polycation (PLL) did not decondense DNA inDNA/PLL (1:3) complexes. Further studies have found that displacementeffects are salt-dependent. In addition, poly-L-glutamic acid but notthe relatively weaker polyanion succinylated poly-L-lysine (SPLL)displaces DNA at higher sodium chloride concentrations. Measurement ofζ-potential of DNA/PLL particles during titration with SPLL revealed thechange of particle surface charge at approximately the chargeequivalency point. Thus, it can be concluded that addition of low chargedensity polyanion to the cationic DNA/PLL particles results in particlesurface charge reversal while maintaining condensed DNA core intact.Finally, DNA/polycation complexes can be both recharged and crosslinkedor caged U.S. Pat. No. 08/778,657, U.S. Pat. No. 09/000,692, U.S. Pat.No. 97/24089, U.S. Pat. No. 09/070299, and U.S. Pat. No. 09/464,871.

[0056] The Use of pH-Sensitive Lipids, Amphipathic Compounds, andLiposomes for Drug and Nucleic Acid Delivery

[0057] After the landmark description of DOTMA(N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride)[Felgner, P L, Gadek, T R, Holm, M, et al. Lipofection: a highlyefficient, lipid-mediated DNA-transfection procedure. Proc. Natl. Acad.Sci. USA. 1987;84:7413-7417], a plethora of cationic lipids have beensynthesized. Basically, all the cationic lipids are amphipathiccompounds that contain a hydrophobic domain, a spacer, andpositively-charged amine. The hydrophobic domains are typicallyhydrocarbon chains such as fatty acids derived from oleic or myristicacid. The hydrocarbon chains are often joined either by ether or esterbonds to a spacer such as glycerol. Quaternary amines often compose thecationic groups. Usually, the cationic lipids are mixed with a fusogeniclipid such as DOPE (dioleoyl phosphatidyl ethanolamine) to formliposomes. The mixtures are mixed in chloroform that is then dried.Water is added to the dried lipid film and unilamellar liposomes formduring sonication. Multilamellar cationic liposomes and cationicliposomes/DNA complexes prepared by the reverse-phase evaporation methodhave also been used for transfection. Cationic liposomes have also beenprepared by an ethanol injection technique.

[0058] Several cationic lipids contain a spermine group for binding toDNA. DOSPA, the cationic lipid within the LipofectAMINE formulation(Life Technologies) contains a spermine linked via a amide bond andethyl group to a trimethyl, quaternary amine [Hawley-Nelson, P,Ciccarone, V and Jessee, J. Lipofectamine reagent: A new, higherefficiency polycationic liposome transfection reagent. Focus1993;15:73-79]. A French group has synthesized a series of cationiclipids such as DOGS (dioctadecylglycinespermine) that contain spermine[Remy, J -S, Sirlin, C, Vierling, P, et al. Gene transfer with a seriesof lipophilic DNA-binding molecules. Bioconjugate Chem. 1994;5:647-654].DNA has also been transfected by lipophilic polylysines which containdipalmotoylsuccinylglycerol chemically-bonded to low molecular weight(˜3000 MW) polylysine [Zhou, X, Kilbanov, A and Huang, L. Lipophilicpolylysines mediate efficient DNA transfection in mammalian cells.Biochim. Biophys. Acta 1991;1065:8-14. Zhou, X and Huang, L. DNAtransfection mediated by cationic liposomes containing lipopolylysine:Characterization and mechanism of action. Biochim. Biophys. Acta 1994;1195-203].

[0059] Other studies have used adjuvants with the cationic liposomes.Transfection efficiency into Cos cells was increased when amphiphilicpeptides derived from influenza virus hemagglutinin were added toDOTMA/DOPE liposomes [Kamata, H, Yagisawa, H, Takahashi, S, et al.Amphiphilic peptides enhance the efficiency of liposome-mediated DNAtransfection. Nucleic Acids Res. 1994;22:536-537]. Cationic lipids havebeen combined with galactose ligands for targeting to the hepatocyteasialoglycoprotein receptor [Remy, J -S, Kichler, A, Mordvinov, V, etal. Targeted gene transfer into hepatoma cells withlipopolyamine-condensed DNA particles presenting galactose ligands: Astage toward artificial viruses. Proc. Natl. Acad. Sci. USA1995;92:1744-1748]. Thiol-reactive phospholipids have also beenincorporated into cationic lipid/pDNA complexes to enable cellularbinding even when the net charge of the complex is not positive[Kichler, A, Remy, J -S, Boussif, O, et al. Efficient gene delivery withneutral complexes of lipospermine and thiol-reactive phospholipids.Biochem. Biophys. Res. Comm. 1995;209:444-450]. DNA-dependent templateprocess converted thiol-containing detergent possessing high criticalmicelle concentration into dimeric lipid-like molecule with apparentlylow water solubility.

[0060] Cationic liposomes may deliver DNA either directly across theplasma membrane or via the endosome compartment. Regardless of its exactentry point, much of the DNA within cationic liposomes does accumulatein the endosome compartment. Several approaches have been investigatedto prevent loss of the foreign DNA in the endosomal compartment byprotecting it from hydrolytic digestion within the endosomes or enablingits escape from endosomes into the cytoplasm. They include the use ofacidotropic (lysomotrophic), weak amines such as chloroquine thatpresumably prevent DNA degradation by inhibiting endosomal acidification[Legendre, J. & Szoka, F. Delivery of plasmid DNA into mammalian celllines using pH-sensitive liposomes: Comparison with cationic liposomes.Pharmaceut. Res. 9, 1235-1242 (1992)]. Viral fusion peptides or wholevirus have been included to disrupt endosomes or promote fusion ofliposomes with endosomes, and facilitate release of DNA into thecytoplasm [Kamata, H., Yagisawa, H., Takahashi, S. & Hirata, H.Amphiphilic peptides enhance the efficiency of liposome-mediated DNAtransfection. Nucleic Acids Res. 22, 536-537 (1994). Wagner, E., Curiel,D. & Cotten, M. Delivery of drugs, proteins and genes into cells usingtransferrin as a ligand for receptor-mediated endocytosis. Advanced DrugDelivery Reviews 14,113-135 (1994)].

[0061] Knowledge of lipid phases and membrane fusion has been used todesign potentially more versatile liposomes that exploit the endosomalacidification to promote fusion with endosomal membranes. Such anapproach is best exemplified by anionic, pH-sensitive liposomes thathave been designed to destabilize or fuse with the endosome membrane atacidic pH [Duzgunes, N., Straubinger, R. M., Baldwin, P. A. &Papahadjopoulos, D. PH-sensitive liposomes. (eds Wilschub, J. &Hoekstra, D.) p. 713-730 (Marcel Deker INC, 1991)]. All of the anionic,pH-sensitive liposomes have utilized phosphatidylethanolamine (PE)bilayers that are stabilized at non-acidic pH by the addition of lipidsthat contain a carboxylic acid group. Liposomes containing only PE areprone to the inverted hexagonal phase (H_(II)). In pH-sensitive, anionicliposomes, the carboxylic acid's negative charge increases the size ofthe lipid head group at pH greater than the carboxylic acid's pK_(a) andthereby stabilizes the-phosphatidylethanolamine bilayer. At acidic pHconditions found within endosomes, the uncharged or reduced chargespecies is unable to stabilize the phosphatidylethanolamine-richbilayer. Anionic, pH-sensitive liposomes have delivered a variety ofmembrane-impermeable compounds including DNA. However, the negativecharge of these pH-sensitive liposomes prevents them from efficientlytaking up DNA and interacting with cells; thus decreasing their utilityfor transfection. We have described the use of cationic, pH-sensitiveliposomes to mediate the efficient transfer of DNA into a variety ofcells in culture U.S. Pat. No. 08/530,598, and U.S. Pat. No. 09/020,566.

[0062] The Use of pH-Sensitive Polymers for Drug and Nucleic AcidDelivery

[0063] Polymers that pH-sensitive are have found broad application inthe area of drug delivery exploiting various physiological andintracellular pH gradients for the purpose of controlled release ofdrugs (both low molecular weight and polymeric). pH sensitivity can bebroadly defined as any change in polymer's physico-chemical propertiesover certain range of pH. More narrow definition demands significantchanges in the polymer's ability to retain (release) a bioactivesubstance (drug) in a physiologically tolerated pH range (usually pH5.5-8). pH-sensitivity presumes the presence of ionizable groups in thepolymer (polyion). All polyions can be divided into three categoriesbased on their ability to donate or accept protons in aqueous solutions:polyacids, polybases and polyampholytes. Use of pH-sensitive polyacidsin drug delivery applications usually relies on their ability to becomesoluble with the pH increase (acid/salt conversion), to form complexwith other polymers over change of pH or undergo significant change inhydrophobicity/hydrophilicity balance. Combinations of all three abovefactors are also possible.

[0064] Copolymers of polymethacrylic acid (Eudragit S, Rohm America) areknown as polymers which are insoluble at lower pH but readilysolubilized at higher pH, so they are used as enteric coatings designedto dissolve at higher intestinal pH (Z Hu et al. J. Drug Target., 7,223, 1999). A typical example of pH-dependent complexation is copolymersof polyacrylate(graft)ethyleneglycol which can be formulated intovarious pH-sensitive hydrogels which exhibit pH-dependent swelling anddrug release (F Madsen et al., Biomaterials, 20, 1701, 1999).Hydrophobically-modified N-isopropylacrylamide-methacrylic acidcopolymer can render regular egg PC liposomes pH-sensitive bypH-dependent interaction of grafted aliphatic chains with lipid bilayer(O Meyer et al., FEBS Lett., 421, 61, 1998). Polymers with pH-mediatedhydrophobicity (like polyethylacrylic acid) can be used as endosomaldisrupters for cytoplasmic drug delivery (Murthy, N., Robichaud, J. R.,Tirrell, D. A., Stayton, P. S., Hoffman, A. S. J. Controlled Release 61,137, 1999).

[0065] Polybases have found broad applications as agents for nucleicacid delivery in transfection/gene therapy applications due to the factthey are readily interact with polyacids. A typical example ispolyethyleneimine (PEI). This polymer secures nucleic acid electrostaticadsorption on the cell surface followed by endocytosis of the wholecomplex. Cytoplasmic release of the nucleic acid occurs presumably viathe so called “proton sponge” effect according to which pH-sensitivityof PEI is responsible for endosome rupture due to osmotic swellingduring its acidification (O Boussif et al. Proc. Natl. Acad. Sci. USA92, 7297, 1995). Cationic acrylates possess the similar activity (forexample, poly-((2-dimethylamino)ethyl methacrylate) (P van de Weteringet al. J. Controlled Release 64, 193, 2000). However, polybases due totheir polycationic nature pH-sensitive polybases have not found broad invivo application so far, due to their acute systemic toxicity in vivo (JH Senior, Biochim. Biophys. Acta, 1070, 173, 1991). Milder polybases(for example, linear PEI) are better tolerated and can be usedsystemically for in vivo gene transfer (D Goula et al. Gene Therapy 5,712, 1998).

[0066] Membrane Active Compounds

[0067] Many biologically active compounds, in particular large and/orcharged compounds, are incapable of crossing biological membranes. Inorder for these compounds to enter cells, the cells must either takethem up by endocytosis, into endosomes, or there must be a disruption ofthe cellular membrane to allow the compound to cross. In the case ofendosomal entry, the endosomal membrane must be disrupted to allow forthe entrance of the compound in the interior of the cell. Therefore,either entry pathway into the cell requires a disruption of the cellularmembrane. There exist compounds termed membrane active compounds thatdisrupt membranes. One can imagine that if the membrane active agentwere operative in a certain time and place it would facilitate thetransport of the biologically active compound across the biologicalmembrane. The control of when and where the membrane active compound isactive is crucial to effective transport. If the membrane activecompound is too active or active at the wrong time, then no transportoccurs or transport is associated with cell rupture and thereby celldeath. Nature has evolved various strategies to allow for membranetransport of biologically active compounds including membrane fusion andthe use membrane active compounds whose activity is modulated such thatactivity assists transport without toxicity. Many lipid-based transportformulations rely on membrane fusion and some membrane active peptides'activities are modulated by pH. In particular, viral coat proteins areoften pH-sensitive, inactive at neutral or basic pH and active under theacidic conditions found in the endosome.

[0068] Small Molecular Endosomolytic Agents

[0069] A cellular transport step that has attracted attention for genetransfer is that of DNA release from intracellular compartments such asendosomes (early and late), lysosomes, phagosomes, vesicle, endoplasmicreticulum, golgi apparatus, trans golgi network (TGN), and sarcoplasmicreticulum. Release includes movement out of an intracellular compartmentinto cytoplasm or into an organelle such as the nucleus. A number ofchemicals such as chloroquine, bafilomycin or Brefeldin A1 have beenused to disrupt or modify the trafficking of molecules throughintracellular pathways. Chloroquine decreases the acidification of theendosomal and lysosomal compartments but also affects other cellularfunctions. Brefeldin A, an isoprenoid fungal metabolite, collapsesreversibly the Golgi apparatus into the endoplasmic reticulum and theearly endosomal compartment into the trans-Golgi network (TGN) to formtubules. Bafilomycin A₁, a macrolide antibiotic is a more specificinhibitor of endosomal acidification and vacuolar type H⁺-ATPase thanchloroquine.

[0070] Viruses, Proteins and Peptides for Disruption of Endosomes andEndosomal Function

[0071] Viruses such as adenovirus have been used to induce gene releasefrom endosomes or other intracellular compartments (D. Curiel, Agarwal,S., Wagner, E., and Cotten, M. PNAS 88:8850, 1991). Rhinovirus has alsobeen used for this purpose (W. Zauner et al. J. Virology 69:1085-92,1995). Viral components such as influenza virus hemagglutinin subunitHA-2 analogs has also been used to induce endosomal release (E. Wagneret al. PNAS 89:7934, 1992). Amphipathic peptides resembling theN-terminal HA-2 sequence has been studied (K. Mechtler and E. Wagner,New J. Chem. 21:105-111, 1997). Parts of the pseudonmonas exotoxin anddiptheria toxin have also been used for drug delivery (I. Pastan and D.FitzGerald. J. Biol. Chem. 264:15157, 1989).

[0072] A variety of synthetic amphipathic peptides have been used toenhance transfection of genes (N. Ohmori et al. Biochem. Biophys. Res.Commun. 235:726, 1997). The ER-retaining signal (KDEL sequence) has beenproposed to enhance delivery to the endoplasmic reticulum and preventdelivery to lysosomes (S. Seetharam et al. J. Biol. Chem. 266:17376,1991).

[0073] The present invention provides for a new group of membrane activecompounds that can enhance the delivery of nucleic acids.

[0074] Other Cellular and Intracellular Gradients Useful for Delivery

[0075] Nucleic acid and gene delivery may involve the biological pHgradient that is active within organisms as a factor in delivering apolynucleotide to a cell. Different pathways that may be affected by thepH gradient include cellular transport mechanisms, endosomaldisruption/breakdown, and particle disassembly (release of the DNA).Other gradients that can be useful in gene therapy research involveionic gradients that are related to cells. For example, both Na⁺ and K⁺have large concentration gradients that exist across the cell membrane.Systems containing metal-binding groups can utilize such gradients toinfluence delivery of a polynucleotide to a cell. Changes in the osmoticpressure in the endosome also have been used to disrupt membranes andallow for transport across membrane layer. Buffering of the endosome pHmay cause these changes in osmotic pressure. For example, the “protonsponge” effect of PEI (O Boussif et al. Proc. Natl. Acad. Sci. USA 92,7297, 1995) and certain polyanions (Murthy, N., Robichaud, J. R.,Tirrell, D. A., Stayton, P. S., Hoffman, A. S. Journal of ControlledRelease 1999, 61, 137) are postulated to cause an increase in the ionicstrength inside of the endosome, which causes a increase in osmoticpressure. This pressure increase results in membrane disruption andrelease of the contents of the endosome.

[0076] In addition to pH and other ionic gradients, there exist otherdifference in the chemical environment associated with cellularactivities that may be used in gene delivery. In particular enzymaticactivity both extra and intracellularly may be used to deliver the geneof interest either by aiding in the delivery to the cell or escape fromintracellular compartments. Proteases, found in serum, lysosome andcytoplasm, may be used to disrupt the particle and allow its interactionwith the cell surface or cause it fracture the intracellularcompartment, e.g. endosome or lysosome, allowing the gene to be releasedintracellularly.

SUMMARY

[0077] Compounds and methods are described for enhancing the delivery ofbiologically active compounds including peptides, small molecular drugsand nucleic acids. Novel pH-labile and membrane active compounds aredescribed. Some of these compounds are cleaved at acidic pH; therebyincreasing their membrane activity. Some of these novel compounds alsohave use as detergents.

DETAILED DESCRIPTION

[0078] The present invention relates to the delivery of desiredcompounds (e.g., drugs and nucleic acids) into cells using pH-labilepolymers and membrane active compounds coupled with labile compounds.The present invention provides compositions and methods for delivery andrelease of a compound of interest to a cell.

[0079] Noncovalent molecule-molecule interactions, which are the basisof DNA-polycation particle formation, rely on discreet interactionsbetween the functional groups on the interacting molecules. It is quiteapparent that if one modifies the interacting functional groups, onechanges the whole molecule-molecule interaction. This is true for smallmolecules and large macromolecules. For example methyl alcohol is aliquid capable of hydrogen bonding with water, which confers thecompound with water solubility. In contrast, conversion of the alcoholfunctional group to a methyl ether to form dimethyl ether renders themolecule in to a water insoluble gas. Many other examples may beobserved in small molecular weight drug-receptor interactions. DNAinteracts with the polycation poly-L-lysine to form condensed DNAparticles. If the amino groups of poly-L-lysine are converted tocarboxylate groups as in succinylated poly-L-lysine there is nointeraction with the polyanion DNA. The identities of the functionalgroups on a molecule dictate its interactions with other molecules.Therefore, the ability to control the identity of the function groups ona molecule allows one to control its interactions. As a consequence,controlled and reversible functional group modification is important ifone want to modulate a molecule's interactions. This control is ofparticular importance when the molecule in question is biologicallyactive. For example, one may not want to administer cytotoxic drugsdirectly. In this case, one may administer a prodrug that is itselfinactive, but becomes active by change(s) in functional group(s) afterdelivery.

[0080] Prior to the present invention, delivery systems suffered fromslow reversibility—or irreversibility—and/or high toxicity. For example,many cationic polymers such as poly-L-lysine (PLL) and polyethylenimine(PEI) form positively charged condensed particles with DNA. In vitro,these particles are relatively good reagents, compared to DNA alone, forthe transfer of DNA into cells. However, these particles are poortransfer reagents in vivo due to their toxicity and relatively stableinteraction with DNA, which renders their complexation irreversibleunder physiological conditions. There are several barriers that thesecomplexes must overcome for them to be efficient gene transfer reagents:stable enough to protect the DNA from nucleases and aid in delivery tothe cell, yet the DNA polycation complex must be disrupted—therebyallowing transcription to occur. Additionally, if the complex is takeninto the cell through the process of endocytosis, the complex mustescape the endosome before being taken into the lysosome and beingdigested.

[0081] To increase the stability of DNA particles in serum, certainembodiments of the present invention provide polyanions that form athird layer in the DNA-polycation complex and it is negatively charged.To assist in the disruption of the DNA complexes, certain embodiments ofthe present invention provide synthesized polymers that are cleaved inthe acid conditions found in the endosome (i.e., pH 5-7). For example,the present invention provides for the cleavage or alteration of alabile chemical group once the complex is in the desired environment:cleavage of the polymer backbone resulting in smaller polyions orcleavage of the link between the polymer backbone and the ion resultingin an ion and an polymer. In either case, the number of molecules in theendosome increases. This alteration may facilitate the release of thedelivered compound into the cytoplasm. Although it is not necessary tounderstand the mechanism in order to use the present invention, and itis not intended that the present invention be so limited, one cancontemplate a number of mechanisms by which the delivery is enhanced bythe present invention. In some instances cleavage of the labile polymerleads to release and enhanced delivery of the therapeutic agent(biologically active compound). Cleavage can also lead to enhancedmembrane activity so that the pharmaceutical (biologically activecompound) is more effectively delivered to the cell. This can occur inthe environs of a tumor or inflamed tissue or within an acidicsub-cellular compartment. Cleavage can also cause an osmotic shock tothe endosomes and disrupts the endosomes. If the polymer backbone ishydrophobic it may interact with the membrane of the endosome. Eithereffect disrupts the endosome and thereby assists in release of deliveredcompound.

[0082] In some embodiments of the present invention, membrane activeagents are complexed with the delivery system such that they areinactive and not membrane active within the complex but become activewhen released, following the chemical conversion of the labile group.The membrane active agents may be used to assist in the disruption ofthe endosome or other cellular compartment. They can also be used toenable selective delivery or toxicity to tumors or tissues that areacidic. Many membrane active agents such as the peptides melittin andpardaxin and various viral proteins and peptides are effective inallowing a disruption of cellular compartments such as endosomes toeffect a release of its contents into a cell. However, these agents aretoxic to cells both in vitro and in vivo due to the inherent nature oftheir membrane activity. To decrease the toxicity of these agents, thepresent invention provides techniques to complex or modify the agent ina way which blocks or inhibits the membrane activity of the agent but isreversible in nature so activity can be recovered when membrane activityis needed for transport of biologically active compound. The activitiesof these membrane active agents can be controlled in a number ofdifferent ways. For example, a modification of the agent may be madethat can be cleaved off of the agent allowing the activity to return.The cleavage can occur during a natural process, such as the pH dropseen in endosomes or cleaved in the cytoplasm of cells where amounts ofreducing agents become available. Cleavage of a blocking agent can occurby delivery of a cleaving agent to the blocked complex at a time when itwould be most beneficial. Another exemplary method of blocking membraneactive agents is to reversibly modify the agents' functional group withan activity blocking addition (defined as “Compounds or ChemicalMoieties that Inhibit or Block the Membrane Activity of Another Compoundor Chemical Moiety”. When the blocking addition reaches an environmentor an adjunct is added the reversible modification is reversed and themembrane active agent will regain activity.

[0083] In some embodiments the biologically active compound isreversibly modified, or complexed with, an interaction modifier suchthat the interactions between the biologically active molecule and itsenvirons, that is its interactions with itself and other molecules, isaltered when the interaction modifier is released. For exampleattachment of such nonionic hydrophilic groups such as polyethyleneglycol and polysaccharides (e.g. starch) may decrease self-associationand interactions with other molecules such as serum compounds andcellular membranes, which may be necessary for transport of thebiologically active molecule to the cell. However these molecules mayinhibit cellular uptake and therefore, must be lost before cellularuptake can occur. Likewise, cell targeting ligands aid in transport to acell but may not be necessary, and may inhibit, transport into a cell.In all of these cases, the reversible attachment of the interactionmodifier, through a labile bond, would be beneficial.

[0084] The present invention provides for the transfer ofpolynucleotides, and other biologically active compounds into cells inculture (also known as “in vitro”). Compounds or kits for thetransfection of cells in culture is commonly sold as “transfectionreagents” or “transfection kits”. The present invention also providesfor the transfer of polynucleotides, and biologically active compoundsinto cells within tissues in situ and in vivo, and deliveredintravasculary (U.S. patent application Ser. No. 08/571,536),intrarterially, intravenous, orally, intraduodenaly, via the jejunum (orileum or colon), rectally, transdermally, subcutaneously,intramuscularly, intraperitoneally, intraparenterally, via directinjections into tissues such as the liver, lung, heart, muscle, spleen,pancreas, brain (including intraventricular), spinal cord, ganglion,lymph nodes, lymphatic system, adipose tissues, thryoid tissue, adrenalglands, kidneys, prostate, blood cells, bone marrow cells, cancer cells,tumors, eye retina, via the bile duct, or via mucosal membranes such asin the mouth, nose, throat, vagina or rectum or into ducts of thesalivary or other exocrine glands. Compounds for the transfection ofcells in vivo in a whole organism can be sold as “in vivo transfectionreagents” or “in vivo transfection kits” or as a pharmaceutical for genetherapy.

[0085] Polymers with pH-Labile Bonds

[0086] The present invention provides a wide variety of polymers withlabile groups that find use in the delivery systems of the presentinvention. The labile groups are selected such that they undergo achemical transformation (e.g., cleavage) when present in physiologicalconditions. The chemical transformation may be initiated by the additionof a compound to the cell or may occur spontaneously when introducedinto intra-and/or extra-cellular environments (e.g., the lower pHconditions of an endosome or the extracellular space surroundingtumors). The conditions under which a labile group will undergotransformation can be controlled by altering the chemical constituentsof the molecule containing the labile group. For example, addition ofparticular chemical moieties (e.g., electron acceptors or donors) nearthe labile group can effect the particular conditions (e.g., pH) underwhich chemical transformation will occur.

[0087] In certain embodiments, the present invention provides compounddelivery systems composed of polymers (e.g., cationic polymers, anionicpolymers, zwitterionic and nonionic polymers) that contain pH-labilegroups. The systems are relatively chemically stable until they areintroduced into acidic conditions that render them unstable (labile). Anaqueous solution is acidic when the concentration of protons (H⁺) exceedthe concentration of hydroxide (OH⁻). Upon delivery to the desiredlocation, the labile group undergoes an acid-catalyzed chemicaltransformation resulting in release of the delivered compound or acomplex of the delivered compound. The pH-labile bond may either be inthe main-chain or in the side chain. If the pH-labile bond occurs in themain chain, then cleavage of the labile bond results in a decrease inpolymer length. If the pH-labile bond occurs in the side chain, thencleavage of the labile bond results in loss of side chain atoms from thepolymer.

[0088] In some preferred embodiments of the present invention, nucleicacids are delivered to cells by a polymer complex containing a labilegroup, or groups, that undergoes chemical transformation when exposed tothe low pH environment of an endosome. Such complexes provide improvednucleic acid delivery systems, as they provide for efficient deliveryand low toxicity.

[0089] Polymers Containing Several Membrane Active Compounds

[0090] The present invention specifies polymers containing more than twomembrane active compounds. In one embodiment, the membrane activecompounds are grafted onto a preformed polymer to form a comb-typepolymer, i.e. a polymer containing side chain groups. In anotherembodiment, the membrane active compounds are incorporated into thepolymer by chain or step polymerization processes. To aid incomplexation between DNA and membrane active compounds and/or to augmentthe membrane activity of membrane active agents, certain embodiments ofthe present invention have polymers composed of monomers that arethemselves membrane active. These polymers are formed by attaching amembrane active compound to a preformed polymer or by polymerization ofmembrane active monomers.

[0091] Membrane Active Compounds Containing Labile Bonds

[0092] The inclusion of labile bonds into membrane active compoundsincreases their versatility in a number of ways. It can reduce theirtoxicity by enabling their membrane activity to be expressed in specifictissues such as tumors and inflamed joints, specific sub-cellularlocations such as endosomes and lysosomes, or under specific conditionssuch as a reducing environment. In one embodiment of the invention, thelabile bonds are pH-sensitive in that the bonds break or are cleavedwhen pH of their microenvironment drops below physiologic pH of 7.4 orbelow pH of 6.5 or below pH of 5.5. In another embodiment the labilebonds are very pH-sensitive. In yet another embodiment, the labile bondsare disulfides that are labile under physiologic conditions or that arecleaved by the addition of an exogenous reducing agent. In otherembodiments, the labile bonds are acetals, ketals, enol ethers, enolesters, amides of 2,3-disubstituted maleamic acid, imines, imminiums,enamines, silyl ethers, and silyl enol ethers.

[0093] The invention also includes compounds that are of the generalstructure: A-B—C wherein A is a membrane active compound, B is a labilelinkage, and C is a compound that inhibits the membrane activity ofcompound A. Upon cleavage of B, membrane activity is restored tocompound A. This cleavage occurs in certain tissue, organ, andsub-cellular locations that are controlled by the microenvironment ofthe location and also by the addition of exogenous agents. In anotherembodiment, the invention includes compositions containing biologicallyactive compounds and compounds of the general structure: A-B—C wherein Ais a membrane active compound, B is a labile linkage, and C is acompound that inhibits the membrane activity of compound A. Thebiologically-active compounds include pharmaceutical drugs, nucleicacids and genes. In yet another embodiment, these compounds that are ofthe general structure—A-B—C wherein A is a membrane active compound, Bis a labile linkage, and C is a compound that inhibits the membraneactivity of compound A- .are used to deliver biologically activecompounds that include pharmaceutical drugs, nucleic acids and genes. Inone specific embodiment, these A-B—C compounds are used to delivernucleic acids and genes to muscle (skeletal, heart, respiratory,striated, and non-striated), liver (hepatocytes), spleen, immune cells,gastrointestinal cells, cells of the nervous system (neurons, glial, andmicroglial), skin cells (dermis and epidermis), joint and synovialcells, tumor cells, kidney, cells of the immune system (dendiritic, Tcells, B cells, antigen-presenting cells, macrophages), exocrine cells(pancreas, salivary glands), prostate, adrenal gland, thyroid gland, eyestructures (retinal cells), and respiratory cells (cells of the lung,nose, respiratory tract)

[0094] Mixtures of Membrane Active Compounds and Labile Compounds

[0095] In addition, the invention is a composition of matter thatincludes a membrane active compound and a labile compound. In oneembodiment, the labile compound inhibits the membrane activity of themembrane active compound. Upon chemical modification of the labilecompound, membrane activity is restored to the membrane active compound.This chemical modification occurs in certain tissue, organ, andsub-cellular locations that are controlled by the microenvironment ofthe location and also by the addition of exogenous agents. In oneembodiment the chemical modification involves the cleavage of thepolymer. In one embodiment, the membrane active compound and theinhibitory labile compound are polyions and are of opposite charge. Forexample, the membrane active compound is a polycation and the inhibitorylabile compound is a polyanion.

[0096] In another embodiment, the invention includes compositionscontaining biologically active compounds, a membrane active compound anda labile compound. Upon chemical modification of the labile compound,membrane activity is restored to the membrane active compound. Thischemical modification occurs in certain tissue, organ, and sub-cellularlocations that are controlled by the microenvironment of the locationand also by the addition of exogenous agents. In one embodiment thechemical modification involves the cleavage of the polymer. In onespecific embodiment, these compositions containing biologically activecompounds, a membrane active compound and a labile compound are used todeliver nucleic acids and genes to muscle (skeletal, heart, respiratory,striated, and non-striated), liver (hepatocytes), spleen, immune cells,gastrointestinal cells, cells of the nervous system (neurons, glial, andmicroglial), skin cells (dermis and epidermis), joint and synovialcells, tumor cells, kidney, cells of the immune system (dendiritic, Tcells, B cells, antigen-presenting cells, macrophages), exocrine cells(pancreas, salivary glands), prostate, adrenal gland, thyroid gland, eyestructures (retinal cells), respiratory cells (cells of the lung, nose,respiratory tract), and endothelial cells.

[0097] Biologically Active Compounds Containing pH-Labile and/orExtremely and/or Very pH-Labile Bonds

[0098] The invention specifies compounds of the following generalstructure: A-B—C wherein A is a biologically active compound such aspharmaceuticals, drugs, proteins, peptides, hormones, cytokines, enzymesand nucleic acids such as anti-sense, ribozyme, recombining nucleicacids, and expressed genes; B is a labile linkage that contains apH-labile bond such as acetals, ketals, enol ethers, enol esters, amidesof 2,3-disubstituted maleamic acids, imines, imminiums, enamines, silylethers, and silyl enol ethers; and C is a compound. In one embodiment Cis a compound that modifies the activity, function, delivery, transport,shelf-life, pharmacokinetics, blood circulation time in vivo, tissue andorgan targetting, and sub-cellular targeting of the biologically activecompound A. For example, C can be a hydrophilic compound such aspolyethylene glycol to increase the water solubility of relativelyhydrophobic drugs (e.g. amphotericin B) to improve their formulation anddelivery properties. In other embodiments, B is a labile linkage thatcontains pH-labile bond such as acetals, ketals, enol ethers, enolesters, amides, imines, imminiums, enamines, silyl ethers, and silylenol ethers.

[0099] The invention also specifies that the labile linkage B isattached to reactive functional groups on the biologically activecompound A. In yet another embodiment, reactive functional groups areattached to nucleic acids via alkylation. Specifically, nitrogen andsulfur mustards may be used for modify nucleic acids with reactivefunctional groups.

[0100] pH-Labile Amphipathic Compounds

[0101] In one specification of the invention, the pH-labile and verypH-labile linkages and bonds are used within amphipathic compounds anddetergents. The pH-labile amphipathic compounds can be incorporated intoliposomes for delivery of biologically active compounds and nucleicacids to cells. The detergents can be used for cleaning purposes and formodifying the solubility of biologically active compounds such asproteins. The detergents can be in the form of micelles or reversemicelles. Often detergents are used to extract biologically activecompounds from natural mixtures. After the extraction procedure iscompleted, a labile detergent would aid in the separation of thedetergent and the biologically active compound. If the detergent islabile under conditions that do not harm the biologically activecompound (e.g. destroying or denaturing a protein), then removal of thedetergent would be much easier that currently-used methods.

[0102] Definitions

[0103] To facilitate an understanding of the present invention, a numberof terms and phrases are defined below:

[0104] Biologically Active Compound

[0105] A biologically active compound is a compound having the potentialto react with biological components. More particularly, biologicallyactive compounds utilized in this specification are designed to changethe natural processes associated with a living cell. For purposes ofthis specification, a cellular natural process is a process that isassociated with a cell before delivery of a biologically activecompound. In this specification, the cellular production of, orinhibition of a material, such as a protein, caused by a human assistinga molecule to an in vivo cell is an example of a delivered biologicallyactive compound. Pharmaceuticals, proteins, peptides, polypeptides,enzyme inhibitors, hormones, cytokines, antigens, viruses,oligonucleotides, enzymes and nucleic acids are examples of biologicallyactive compounds.

[0106] Peptide and polypeptide refer to a series of amino acid residues,more than two, connected to one another by amide bonds between the betaor alpha-amino group and carboxyl group of contiguous amino acidresidues. The amino acids may be naturally occurring or synthetic.Polypeptide includes proteins and peptides, modified proteins andpeptides, and non-natural proteins and peptides. Enzymes are proteinsevolved by the cells of living organisms for the specific function ofcatalyzing chemical reactions. A chemical reaction is defined as theformation or cleavage of covalent or ionic bonds. Bioactive compoundsmay be used interchangeably with biologically active compound forpurposes of this application.

[0107] Delivery of Biologically Active Compound

[0108] The delivery of a biologically active compound is commonly knownas “drug delivery”. “Delivered” means that the biologically activecompound becomes associated with the cell or organism. The compound canbe in the circulatory system, intravessel, extracellular, on themembrane of the cell or inside the cytoplasm, nucleus, or otherorganelle of the cell.

[0109] Parenteral routes of administration include intravascular(intravenous, intraarterial), intramuscular, intraparenchymal,intradermal, subdermal, subcutaneous, intratumor, intraperitoneal,intrathecal, subdural, epidural, and intralymphatic injections that usea syringe and a needle or catheter. An intravascular route ofadministration enables a polymer or polynucleotide to be delivered tocells more evenly distributed and more efficiently expressed than directinjections. Intravascular herein means within a tubular structure calleda vessel that is connected to a tissue or organ within the body. Withinthe cavity of the tubular structure, a bodily fluid flows to or from thebody part. Examples of bodily fluid include blood, cerebrospinal fluid(CSF), lymphatic fluid, or bile. Examples of vessels include arteries,arterioles, capillaries, venules, sinusoids, veins, lymphatics, and bileducts. The intravascular route includes delivery through the bloodvessels such as an artery or a vein. An administration route involvingthe mucosal membranes is meant to include nasal, bronchial, inhalationinto the lungs, or via the eyes. Other routes of administration includeintraparenchymal into tissues such as muscle (intramuscular), liver,brain, and kidney. Transdermal routes of administration have beeneffected by patches and ionotophoresis. Other epithelial routes includeoral, nasal, respiratory, and vaginal routes of administration.

[0110] Delivery System

[0111] Delivery system is the means by which a biologically activecompound becomes delivered. That is all compounds, including thebiologically active compound itself, that are required for delivery andall procedures required for delivery including the form (such volume andphase (solid, liquid, or gas)) and method of administration (such as butnot limited to oral or subcutaneous methods of delivery).

[0112] Nucleic Acid

[0113] The term “nucleic acid” is a term of art that refers to a polymercontaining at least two nucleotides. “Nucleotides” contain a sugardeoxyribose (DNA) or ribose (RNA), a base, and a phosphate group.Nucleotides are linked together through the phosphate groups. “Bases”include purines and pyrimidines, which further include natural compoundsadenine, thymine, guanine, cytosine, uracil, inosine, and naturalanalogs, and synthetic derivatives of purines and pyrimidines, whichinclude, but are not limited to, modifications which place new reactivegroups such as, but not limited to, amines, alcohols, thiols,carboxylates, and alkylhalides. Nucleotides are the monomeric units ofnucleic acid polymers. A “polynucleotide” is distinguished here from an“oligonucleotide” by containing more than 80 monomeric units;oligonucleotides contain from 2 to 80 nucleotides. The term nuclei acidincludes deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Theterm encompasses sequences that include any of the known base analogs ofDNA and RNA including, but not limited to, 4-acetylcytosine,8-hydroxy-N6-methyladenosine, aziridinylcytosine, pseudoisocytosine,5-(carboxyhydroxylmethyl) uracil, 5-fluorouracil, 5-bromouracil,5-carboxymethylaminomethyl-2-thiouracil,5-carboxymethylaminomethyluracil, dihydrouracil, inosine,N6-isopentenyladenine, 1-methyladenine, 1-methylpseudouracil,1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2-methyladenine,2-methylguanine, 3-methylcytosine, 5-methylcytosine, N6-methyladenine,7-methylguanine, 5-methylaminomethyluracil,5-methoxyaminomethyl-2-thiouracil, beta-D-mannosylqueosine,5′-methoxycarbonylmethyluracil, 5-methoxyuracil,2-methylthio-N6-isopentenyladenine, uracil-5-oxyacetic acid methylester,uracil-5-oxyacetic acid, oxybutoxosine, pseudouracil, queosine,2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil,5-methyluracil, N-uracil-5-oxyacetic acid methylester,uracil-5-oxyacetic acid, pseudouracil, queosine, 2-thiocytosine, and2,6-diaminopurine.

[0114] DNA may be in the form of anti-sense, plasmid DNA, parts of aplasmid DNA, product of a polymerase chain reaction (PCR), vectors (P1,PAC, BAC, YAC, artificial chromosomes), expression cassettes, chimericsequences, chromosomal DNA, or derivatives of these groups. RNA may bein the form of oligonucleotide RNA, tRNA (transfer RNA), snRNA (smallnuclear RNA), rRNA (ribosomal RNA), mRNA (messenger RNA), anti-senseRNA, ribozymes, chimeric sequences, or derivatives of these groups.

[0115] “Anti-sense” is a polynucleotide that interferes with thefunction of DNA and/or RNA. This may result in suppression ofexpression. Natural nucleic acids have a phosphate backbone, artificialnucleic acids may contain other types of backbones and bases. Theseinclude PNAs (peptide nucleic acids), phosphothionates, and othervariants of the phosphate backbone of native nucleic acids. In addition,DNA and RNA may be single, double, triple, or quadruple stranded.

[0116] The term “recombinant DNA molecule” as used herein refers to aDNA molecule that is comprised of segments of DNA joined together bymeans of molecular biological techniques. “Expression cassette” refersto a natural or recombinantly produced polynucleotide molecule that iscapable of expressing protein(s). A DNA expression cassette typicallyincludes a promoter (allowing transcription initiation), and a sequenceencoding one or more proteins. Optionally, the expression cassette mayinclude transcriptional enhancers, non-coding sequences, splicingsignals, transcription termination signals, and polyadenylation signals.An RNA expression cassette typically includes a translation initiationcodon (allowing translation initiation), and a sequence encoding one ormore proteins. Optionally, the expression cassette may includetranslation termination signals, a polyadenosine sequence, internalribosome entry sites (IRES), and non-coding sequences.

[0117] A nucleic acid can be used to modify the genomic orextrachromosomal DNA sequences. This can be achieved by delivering anucleic acid that is expressed. Alternatively, the nucleic acid caneffect a change in the DNA or RNA sequence of the target cell. This canbe achieved by homologous recombination, gene conversion, or other yetto be described mechanisms.

[0118] Gene

[0119] The term “gene” refers to a nucleic acid (e.g., DNA) sequencethat comprises coding sequences necessary for the production of apolypeptide or precursor (e.g., -myosin heavy chain). The polypeptidecan be encoded by a full length coding sequence or by any portion of thecoding sequence so long as the desired activity or functional properties(e.g., enzymatic activity, ligand binding, signal transduction, etc.) ofthe full-length or fragment are retained. The term also encompasses thecoding region of a structural gene and the including sequences locatedadjacent to the coding region on both the 5′ and 3′ ends for a distanceof about 1 kb or more on either end such that the gene corresponds tothe length of the full-length mRNA. The sequences that are located 5′ ofthe coding region and which are present on the mRNA are referred to as5′ non-translated sequences. The sequences that are located 3′ ordownstream of the coding region and which are present on the mRNA arereferred to as 3′ non-translated sequences. The term “gene” encompassesboth cDNA and genomic forms of a gene. A genomic form or clone of a genecontains the coding region interrupted with non-coding sequences termed“introns” or “intervening regions” or “intervening sequences.” Intronsare segments of a gene which are transcribed into nuclear RNA (hnRNA);introns may contain regulatory elements such as enhancers. Introns areremoved or “spliced out” from the nuclear or primary transcript; intronstherefore are absent in the messenger RNA (mRNA) transcript. The mRNAfunctions during translation to specify the sequence or order of aminoacids in a nascent polypeptide.

[0120] As used herein, the terms “nucleic acid molecule encoding,” “DNAsequence encoding,” and “DNA encoding” refer to the order or sequence ofdeoxyribonucleotides along a strand of deoxyribonucleic acid. The orderof these deoxyribonucleotides determines the order of amino acids alongthe polypeptide (protein) chain. The DNA sequence thus codes for theamino acid sequence.

[0121] As used herein, the terms “an oligonucleotide having a nucleotidesequence encoding a gene” and “polynucleotide having a nucleotidesequence encoding a gene,” means a nucleic acid sequence comprising thecoding region of a gene or in other words the nucleic acid sequencewhich encodes a gene product. The coding region may be present in eithera cDNA, genomic DNA or RNA form. When present in a DNA form, theoligonucleotide or polynucleotide may be single-stranded ordouble-stranded. Suitable control elements such as enhancers/promoters,splice junctions, polyadenylation signals, etc. may be placed in closeproximity to the coding region of the gene if needed to permit properinitiation of transcription and/or correct processing of the primary RNAtranscript. Alternatively, the coding region utilized in the expressionvectors of the present invention may contain endogenousenhancers/promoters, splice junctions, intervening sequences,polyadenylation signals, etc. or a combination of both endogenous andexogenous control elements.

[0122] The term “isolated” when used in relation to a nucleic acid, asin “an isolated oligonucleotide” or “isolated polynucleotide” refers toa nucleic acid sequence that is identified and separated from at leastone contaminant nucleic acid with which it is ordinarily associated inits natural source. Isolated nucleic acid is such present in a form orsetting that is different from that in which it is found in nature. Incontrast, non-isolated nucleic acids as nucleic acids such as DNA andRNA found in the state they exist in nature. For example, a given DNAsequence (e.g., a gene) is found on the host cell chromosome inproximity to neighboring genes; RNA sequences, such as a specific mRNAsequence encoding a specific protein, are found in the cell as a mixturewith numerous other mRNAs that encode a multitude of proteins. However,isolated nucleic acid encoding a given protein includes, by way ofexample, such nucleic acid in cells ordinarily expressing the givenprotein where the nucleic acid is in a chromosomal location differentfrom that of natural cells, or is otherwise flanked by a differentnucleic acid sequence than that found in nature. The isolated nucleicacid, oligonucleotide, or polynucleotide may be present insingle-stranded or double-stranded form.

[0123] Gene Expression

[0124] As used herein, the term “gene expression” refers to the processof converting genetic information encoded in a gene into RNA (e.g.,mRNA, rRNA, tRNA, or snRNA) through “transcription” of the gene (i.e.,via the enzymatic action of an RNA polymerase), and for protein encodinggenes, into protein through “translation” of mRNA. Gene expression canbe regulated at many stages in the process. “Up-regulation” or“activation” refers to regulation that increases the production of geneexpression products (i.e., RNA or protein), while “down-regulation” or“repression” refers to regulation that decreases production. Molecules(e.g., transcription factors) that are involved in up-regulation ordown-regulation are often called “activators” and “repressors,”respectively.

[0125] Delivery of Nucleic Acids

[0126] The process of delivering a polynucleotide to a cell has beencommonly termed “transfection” or the process of “transfecting” and alsoit has been termed “transformation”. The polynucleotide could be used toproduce a change in a cell that can be therapeutic. The delivery ofpolynucleotides or genetic material for therapeutic and researchpurposes is commonly called “gene therapy”. The delivery of nucleic acidcan lead to modification of the DNA sequence of the target cell.

[0127] The polynucleotides or genetic material being delivered aregenerally mixed with transfection reagents prior to delivery. The term“transfection” as used herein refers to the introduction of foreign DNAinto eukaryotic cells. Transfection may be accomplished by a variety ofmeans known to the art including calcium phosphate-DNA co-precipitation,DEAE-dextran-mediated transfection, polybrene-mediated transfection,electroporation, microinjection, liposome fusion, lipofection,protoplast fusion, retroviral infection, and biolistics.

[0128] The term “stable transfection” or “stably transfected” refers tothe introduction and integration of foreign DNA into the genome of thetransfected cell. The term “stable transfectant” refers to a cell thathas irreversibly integrated foreign DNA into the genomic DNA.

[0129] The term “transient transfection” or “transiently transfected”refers to the introduction of foreign DNA into a cell where the foreignDNA fails to integrate into the genome of the transfected cell. Theforeign DNA persists in the nucleus of the transfected cell for severaldays. During this time the foreign DNA is subject to the regulatorycontrols that govern the expression of endogenous genes in thechromosomes. The term “transient transfectant” refers to cells that havetaken up foreign DNA but have failed to integrate this DNA. The term“naked polynucleotides” indicates that the polynucleotides are notassociated with a transfection reagent or other delivery vehicle that isrequired for the polynucleotide to be delivered to a cell.

[0130] A “transfection reagent” or “delivery vehicle” is a compound orcompounds that bind(s) to or complex(es) with oligonucleotides,polynucleotides, or other desired compounds and mediates their entryinto cells. Examples of transfection reagents include, but are notlimited to, cationic liposomes and lipids, polyamines, calcium phosphateprecipitates, histone proteins, polyethylenimine, and polylysinecomplexes (polyethylenimine and polylysine are both toxic). Typically,when used for the delivery of nucleic acids, the transfection reagenthas a net positive charge that binds to the polynucleotide's negativecharge. For example, cationic liposomes or polylysine complexes have netpositive charges that enable them to bind to DNA or RNA.

[0131] Enzyme

[0132] Enzyme is a protein that acts as a catalyst. That is a proteinthat increases the rate of a chemical reaction without itself undergoingany permanent chemical change. The chemical reactions that are catalyzedby an enzyme are termed enzymatic reactions and chemical reactions thatare not are termed nonenzymatic reactions.

[0133] Half-Life

[0134] The half-life of a chemical reaction is the time required for onehalf of a given material to undergo a chemical reaction.

[0135] Complex

[0136] Two molecules are combined, to form a complex through a processcalled complexation or complex formation, if the are in contact with oneanother through noncovalent interactions such as electrostaticinteractions, hydrogen bonding interactions, and hydrophobicinteractions.

[0137] Modification

[0138] A molecule is modified, to form a modification through a processcalled modification, by a second molecule if the two become bondedthrough a covalent bond. That is, the two molecules form a covalent bondbetween an atom form one molecule and an atom from the second moleculeresulting in the formation of a new single molecule. A chemical covalentbond is an interaction, bond, between two atoms in which there is asharing of electron density.

[0139] Osmosis

[0140] Osmosis is the passage of a solvent through a semipermeablemembrane, a membrane through which solvent can pass but not all solutes,separating two solutions of different concentrations. There is atendency for the separated solutions to become the same concentration asthe solvent passes from low concentration to high concentration. Osmosiswill stop when the two solutions become equal in concentration or whenpressure is applied to the solution containing higher concentration.When the higher concentrated solution is in a closed system, that iswhen system is of constant volume, there is a build up of pressure asthe solvent passes from low to high concentration. This build up ofpressure is called osmotic pressure.

[0141] Salt

[0142] A salt is any compound containing ionic bonds, that is bonds inwhich one or more electrons are transferred completely from one atom toanother.

[0143] Interpolyelectrolyte Complexes

[0144] An interpolyelectrolyte complex is a noncovalent interactionbetween polyelectrolytes of opposite charge.

[0145] Charge, Polarity, and Sign

[0146] The charge, polarity, or sign of a compound refers to whether ornot a compound has lost one or more electrons (positive charge,polarity, or sign) or gained one or more electrons (negative charge,polarity, or sign).

[0147] Cell Targeting Signals

[0148] Cell targeting signal (or abbreviated as the Signal) is definedin this specification as a molecule that modifies a biologically activecompounds such as drug or nucleic acid and can direct it to a celllocation (such as tissue) or location in a cell (such as the nucleus)either in culture or in a whole organism. By modifying the cellular ortissue location of the foreign gene, the function of the biologicallyactive compound can be enhanced.

[0149] The cell targeting signal can be a protein, peptide, lipid,steroid, sugar, carbohydrate, (non-expressing) polynucleic acid orsynthetic compound. The cell targeting signal enhances cellular bindingto receptors, cytoplasmic transport to the nucleus and nuclear entry orrelease from endosomes or other intracellular vesicles.

[0150] Nuclear localizing signals enhance the targeting of thepharmaceutical into proximity of the nucleus and/or its entry into thenucleus. Such nuclear transport signals can be a protein or a peptidesuch as the SV40 large T ag NLS or the nucleoplasmin NLS. These nuclearlocalizing signals interact with a variety of nuclear transport factorssuch as the NLS receptor (karyopherin alpha) which then interacts withkaryopherin beta. The nuclear transport proteins themselves could alsofunction as NLS's since they are targeted to the nuclear pore andnucleus. For example, karyopherin beta itself could target the DNA tothe nuclear pore complex. Several peptides have been derived from theSV40 T antigen. These include a short NLS (H-SEQ ID NO: 2-OH,) or longNLS's (H-SEQ ID NO: 3-OH,; and H-SEQ ID NO: 4-OH,). Other NLS peptideshave been derived from M9 protein (SEQ ID NO: 5), E1A (H-SEQ ID NO:6-OH,), nucleoplasmin (H-SEQ ID NO: 7-OH,), and c-myc (H-SEQ ID NO:8-OH,).

[0151] Signals that enhance release from intracellular compartments(releasing signals) can cause DNA release from intracellularcompartments such as endosomes (early and late), lysosomes, phagosomes,vesicle, endoplasmic reticulum, golgi apparatus, trans golgi network(TGN), and sarcoplasmic reticulum. Release includes movement out of anintracellular compartment into cytoplasm or into an organelle such asthe nucleus. Releasing signals include chemicals such as chloroquine,bafilomycin or Brefeldin A1 and the ER-retaining signal (SEQ ID NO: 9),viral components such as influenza virus hemagglutinin subunit HA-2peptides and other types of amphipathic peptides.

[0152] Cellular receptor signals are any signal that enhances theassociation of the biologically active compound with a cell. This can beaccomplished by either increasing the binding of the compound to thecell surface and/or its association with an intracellular compartment,for example: ligands that enhance endocytosis by enhancing binding thecell surface. This includes agents that target to the asialoglycoproteinreceptor by using asiologlycoproteins or galactose residues. Otherproteins such as insulin, EGF, or transferrin can be used for targeting.Peptides that include the RGD sequence can be used to target many cells.Chemical groups that react with thiol, sulfhydryl, or disulfide groupson cells can also be used to target many types of cells. Folate andother vitamins can also be used for targeting. Other targeting groupsinclude molecules that interact with membranes such as lipids, fattyacids, cholesterol, dansyl compounds, and amphotericin derivatives. Inaddition viral proteins could be used to bind cells.

[0153] Interaction Modifiers

[0154] An interaction modifier changes the way that a molecule interactswith itself or other molecules, relative to molecule containing nointeraction modifier. The result of this modification is thatself-interactions or interactions with other molecules are eitherincreased or decreased. For example cell targeting signals areinteraction modifiers with change the interaction between a molecule anda cell or cellular component. Polyethylene glycol is an interactionmodifier that decreases interactions between molecules and themselvesand with other molecules.

[0155] Reporter or Marker Molecules

[0156] Reporter or marker molecules are compounds that can be easilydetected. Typically they are fluorescent compounds such as fluorescein,rhodamine, Texas red, cy 5, cy 3 or dansyl compounds. They can bemolecules that can be detected by infrared, ultraviolet or visiblespectroscopy or by antibody interactions or by electron spin resonance.Biotin is another reporter molecule that can be detected by labeledavidin. Biotin could also be used to attach targeting groups.

[0157] Linkages

[0158] An attachment that provides a covalent bond or spacer between twoother groups (chemical moieties). The linkage may be electronicallyneutral, or may bear a positive or negative charge. The chemicalmoieties can be hydrophilic or hydrophobic. Preferred spacer groupsinclude, but are not limited to C1-C12 alkyl, C1-C12 alkenyl, C1-C12alkynyl, C6-C18 aralkyl, C6-C18 aralkenyl, C6-C18 aralkynyl, ester,ether, ketone, alcohol, polyol, amide, amine, polyglycol, polyether,polyamine, thiol, thio ether, thioester, phosphorous containing, andheterocyclic.

[0159] Bifunctional

[0160] Bifunctional molecules, commonly referred to as crosslinkers, areused to connect two molecules together, i.e. form a linkage between twomolecules. Bifunctional molecules can contain homo orheterobifunctionality.

[0161] Crosslinking

[0162] Crosslinking refers to the chemical attachment of two or moremolecules with a bifunctional reagent. A bifunctional reagent is amolecule with two reactive ends. The reactive ends can be identical asin a homobifunctional molecule, or different as in a heterobifunctionalmolecule.

[0163] Labile Bond

[0164] A labile bond is a covalent bond that is capable of beingselectively broken. That is, the labile bond may be broken in thepresence of other covalent bonds without the breakage of other covalentbonds. For example, a disulfide bond is capable of being broken in thepresence of thiols without cleavage of any other bonds, such ascarbon-carbon, carbon-oxygen, carbon-sulfur, carbon-nitrogen bonds,which may also be present in the molecule.

[0165] Labile Linkage

[0166] A labile linkage is a chemical compound that contains a labilebond and provides a link or spacer between two other groups. The groupsthat are linked may be chosen from compounds such as biologically activecompounds, membrane active compounds, compounds that inhibit membraneactivity, functional reactive groups, monomers, and cell targetingsignals. The spacer group may contain chemical moieties chosen from agroup that includes alkanes, alkenes, esters, ethers, glycerol, amide,saccharides, polysaccharides, and heteroatoms such as oxygen, sulfur, ornitrogen. The spacer may be electronically neutral, may bear a positiveor negative charge, or may bear both positive and negative charges withan overall charge of neutral, positive or negative.

[0167] pH-Labile Linkages and Bonds

[0168] pH-labile refers to the selective breakage of a covalent bondunder acidic conditions (pH<7). That is, the pH-labile bond may bebroken under acidic conditions in the presence of other covalent bondswithout their breakage. The term pH-labile includes both linkages andbonds that are pH-labile, very pH-labile, and extremely pH-labile.

[0169] Very pH-Labile Linkages and Bonds

[0170] A subset of pH-labile bonds is very pH-labile. For the purposesof the present invention, a bond is considered very pH-labile if thehalf-life for cleavage at pH 5 is less than 45 minutes.

[0171] Extremely pH-Labile Linkages and Bonds

[0172] A subset of pH-labile bonds is extremely pH-labile. For thepurposes of the present invention, a bond is considered extremelypH-labile if the half-life for cleavage at pH 5 is less than 15 minutes.

[0173] Amphiphilic and Amphipathic Compounds

[0174] Amphipathic, or amphiphilic, compounds have both hydrophilic(water-soluble) and hydrophobic (water-insoluble) parts. Hydrophilicgroups indicate in qualitative terms that the chemical moiety iswater-preferring. Typically, such chemical groups are water soluble, andare hydrogen bond donors or acceptors with water. Examples ofhydrophilic groups include compounds with the following chemicalmoieties; carbohydrates, polyoxyethylene, peptides, oligonucleotides andgroups containing amines, amides, alkoxy amides, carboxylic acids,sulfurs, or hydroxyls. Hydrophobic groups indicate in qualitative termsthat the chemical moiety is water-avoiding. Typically, such chemicalgroups are not water soluble, and tend not to hydrogen bonds.Hydrocarbons are hydrophobic groups.

[0175] Detergent

[0176] Detergents or surfactants are water-soluble molecules containinga hydrophobic portion (tail) and a hydrophilic portion (head), whichupon addition to water decrease water's surface tension. The hydrophobicportion can be alkyl, alkenyl, alkynyl or aromatic. The hydrophilicportion can be charged with either net positive (cationic detergents),negative (anionic detergents), uncharged (nonionic detergents), orcharge neutral (zwitterionic detergent). Examples of anionic detergentsare sodium dodecyl sulfate, glycolic acid ethoxylate(4 units)4-tert-butylphenylether, palmitic acid, and oleic acid. Examples ofcationic detergents are cetyltrimethylammonium bromide and oleylamine.Examples of nonionic detergents include, laurylmaltoside, Triton X-100,and Tween. Examples of zwitterionic detergents include3-[(3-cholamidopropyl)dimthylammonio[1-propane-sulfonate (CHAPS), andN-tetradecyl-N,N-dimethyl-3-ammoniu-1-propanesulfonate.

[0177] Surface Tension

[0178] The surface tension of a liquid is the force acting over thesurface of the liquid per unit length of surface that is perpendicularto the force that is acting of the surface. Surface charge has the unitsforce per length, e.g. Newtons/meter.

[0179] Membrane Active Compound

[0180] Membrane active agents or compounds are compounds (typically apolymer, peptide or protein) that are able alter the membrane structure.This change in structure can be shown by the compound inducing one ormore of the following effects upon a membrane: an alteration that allowssmall molecule permeability, pore formation in the membrane, a fusionand/or fission of membranes, an alteration that allows large moleculepermeability, or a dissolving of the membrane. This alteration can befunctionally defined by the compound's activity in at least one thefollowing assays: red blood cell lysis (hemolysis), liposome leakage,liposome fusion, cell fusion, cell lysis and endosomal release. Anexample of a membrane active agent in our examples is the peptidemelittin, whose membrane activity is demonstrated by its ability torelease heme from red blood cells (hemolysis). In addition,dimethylmaleamic-modified melittin(DM-Mel) reverts to melittin in theacidic environment of the endosome causes endosomal release as seen bythe diffuse staining of fluorescein-labeled dextran in our endosomalrelease assay.

[0181] More specifically membrane active compounds allow for thetransport of molecules with molecular weight greater than 50 atomic massunits to cross a membrane. This transport may be accomplished by eitherthe total loss of membrane structure, the formation of holes (or pores)in the membrane structure, or the assisted transport of compound throughthe membrane. In addition, transport between liposomes, or cellmembranes, may be accomplished by the fusion of the two membranes andthereby the mixing of the contents of the two membranes.

[0182] Membrane Active Peptides.

[0183] Membrane active peptides are peptides that have membraneactivity. There are many naturally occurring membrane active peptidessuch as cecropin (insects), magainin, CPF 1, PGLa, Bombinin BLP-1 (allthree from amphibians), melittin (bees), seminalplasmin (bovine),indolicidin, bactenecin (both from bovine neutrophils), tachyplesin 1(crabs), protegrin (porcine leukocytes), and defensins (from human,rabbit, bovine, fungi, and plants). Gramicidin A and gramicidin S(bacillus brevis), the lantibiotics such as nisin (lactococcus lactis),androctonin (scorpion), cardiotoxin I (cobra), caerin (frog litoriasplendida), dermaseptin (frog). Viral peptides have also been shown tohave membrane activity, examples include hemagglutinin subunit HA-2(influenza virus), E1 (Semliki forest virus), F1 (Sendai and measlesviruses), gp41 (HIV), gp32 (SIV), and vp1 (Rhino, polio, and coxsackieviruses). In addition synthetic peptides have also been shown to havemembrane activity. Synthetic peptides that are rich in leucines andlysines (KL or KL_(n) motif) have been shown to have membrane activity.In particular, the peptide H₂N-SEQ ID NO: 10-CO₂, termed KL₃, ismembrane active.

[0184] Compounds or Chemical Groups (Moieties) that Inhibit or Block theMembrane Activity of Another Compound or Chemical Moiety

[0185] An interaction with a membrane active agent by modification orcomplexation (including covalent, ionic, hydrogen bonding, coordination,and van der Waals bonds) with another compound that causes a reduction,or cessation of the said agents membrane activity. Examples include thecovalent modification of a membrane-active peptide by the covalentattachment of an inhibitory chemical group (moiety) to the membraneactive peptide. Another example includes the interpolyelectrolytecomplexation of a membrane active polyanion and inhibitory polycation.

[0186] Polymers

[0187] A polymer is a molecule built up by repetitive bonding togetherof smaller units called monomers. In this application the term polymerincludes both oligomers which have two to about 80 monomers and polymershaving more than 80 monomers. The polymer can be linear, branchednetwork, star, comb, or ladder types of polymer. The polymer can be ahomopolymer in which a single monomer is used or can be copolymer inwhich two or more monomers are used. Types of copolymers includealternating, random, block and graft.

[0188] The main chain of a polymer is composed of the atoms whose bondsare required for propagation of polymer length. For example inpoly-L-lysine, the carbonyl carbon, α-carbon, and α-amine groups arerequired for the length of the polymer and are therefore main chainatoms. The side chain of a polymer is composed of the atoms whose bondsare not required for propagation of polymer length. For example inpoly-L-lysine, the β, γ, δ, and ε-carbons, and ε-nitrogen are notrequired for the propagation of the polymer and are therefore side chainatoms.

[0189] To those skilled in the art of polymerization, there are severalcategories of polymerization processes that can be utilized in thedescribed process. The polymerization can be chain or step. Thisclassification description is more often used that the previousterminology of addition and condensation polymer. “Most step-reactionpolymerizations are condensation processes and most chain-reactionpolymerizations are addition processes” (M. P. Stevens PolymerChemistry: An Introduction New York Oxford University Press 1990).Template polymerization can be used to form polymers from daughterpolymers. Step Polymerization:

[0190] In step polymerization, the polymerization occurs in a stepwisefashion. Polymer growth occurs by reaction between monomers, oligomersand polymers. No initiator is needed since there is the same reactionthroughout and there is no termination step so that the end groups arestill reactive. The polymerization rate decreases as the functionalgroups are consumed. Typically, step polymerization is done either oftwo different ways. One way, the monomer has both reactive functionalgroups (A and B) in the same molecule so that

A-B yields -[A-B]—

[0191] Or the other approach is to have two difunctional monomers.

A-A+B-B yields -[A-A-B—B]—

[0192] Generally, these reactions can involve acylation or alkylation.Acylation is defined as the introduction of an acyl group (—COR) onto amolecule. Alkylation is defined as the introduction of an alkyl grouponto a molecule.

[0193] If functional group A is an amine then B can be (but notrestricted to) an isothiocyanate, isocyanate, acyl azide,N-hydroxysuccinimide, sulfonyl chloride, aldehyde (includingformaldehyde and glutaraldehyde), ketone, epoxide, carbonate,imidoester, carboxylate, or alkylphosphate, arylhalides(difluoro-dinitrobenzene), anhydrides or acid halides, p-nitrophenylesters, o-nitrophenyl pentachlorophenyl esters, or pentafluorophenylesters. In other terms when function A is an amine then function B canbe acylating or alkylating agent or amination.

[0194] If functional group A is a thiol, sulfhydryl, then function B canbe (but not restricted to) an iodoacetyl derivative, maleimide,aziridine derivative, acryloyl derivative, fluorobenzene derivatives, ordisulfide derivative (such as a pyridyl disulfide or5-thio-2-nitrobenzoic acid {TNB} derivatives).

[0195] If functional group A is carboxylate then function B can be (butnot restricted to) a diazoacetate or an amine in which a carbodiimide isused. Other additives may be utilized such as carbonyldiimidazole,dimethylaminopyridine, N-hydroxysuccinimide or alcohol usingcarbodiimide and dimethylaminopyridine.

[0196] If functional group A is a hydroxyl then function B can be (butnot restricted to) an epoxide, oxirane, or an amine in whichcarbonyldiimidazole or N,N′-disuccinimidyl carbonate, orN-hydroxysuccinimidyl chloroformate or other chloroformates are used.

[0197] If functional group A is an aldehyde or ketone then function Bcan be (but not restricted to) an hydrazine, hydrazide derivative, amine(to form a imine or iminium that may or may not be reduced by reducingagents such as NaCNBH₃) or hydroxyl compound to form a ketal or acetal.

[0198] Yet another approach is to have one difunctional monomer so that

A-A plus another agent yields -[A-A]-.

[0199] If function A is a thiol, sulfhydryl, group then it can beconverted to disulfide bonds by oxidizing agents such as iodine (I₂) orNaIO₄ (sodium periodate), or oxygen (O₂). Function A can also be anamine that is converted to a thiol, sulfhydryl, group by reaction with2-Iminothiolate (Traut's reagent) which then undergoes oxidation anddisulfide formation. Disulfide derivatives (such as a pyridyl disulfideor 5-thio-2-nitrobenzoic acid {TNB} derivatives) can also be used tocatalyze disulfide bond formation.

[0200] Functional group A or B in any of the above examples could alsobe a photoreactive group such as aryl azides, halogenated aryl azides,diazo, benzophenones, alkynes or diazirine derivatives.

[0201] Reactions of the amine, hydroxyl, thiol, sulfhydryl, carboxylategroups yield chemical bonds that are described as amide, amidine,disulfide, ethers, esters, enamine, urea, isothiourea, isourea,sulfonamide, carbamate, carbon-nitrogen double bond (imine), alkylaminebond (secondary amine), carbon-nitrogen single bonds in which the carboncontains a hydroxyl group, thio-ether, diol, hydrazone, diazo, orsulfone.

[0202] Chain Polymerization: In chain-reaction polymerization growth ofthe polymer occurs by successive addition of monomer units to limitednumber of growing chains. The initiation and propagation mechanisms aredifferent and there is usually a chain-terminating step. Thepolymerization rate remains constant until the monomer is depleted.

[0203] Monomers containing vinyl, acrylate, methacrylate, acrylamide,methacrylamide groups can undergo chain reaction, which can be radical,anionic, or cationic. Chain polymerization can also be accomplished bycycle or ring opening polymerization. Several different types of freeradical initiatiors could be used that include peroxides, hydroxyperoxides, and azo compounds such as 2,2′-Azobis(-amidinopropane)dihydrochloride (AAP). A compound is a material made up of two or moreelements.

[0204] Types of Monomers: A wide variety of monomers can be used in thepolymerization processes. These include positive charged organicmonomers such as amines, imidine, guanidine, imine, hydroxylamine,hydrazine, heterocycles (like imidazole, pyridine, morpholine,pyrimidine, or pyrene. The amines could be pH-sensitive in that thepK_(a) of the amine is within the physiologic range of 4 to 8. Specificamines include spermine, spermidine,N,N′-bis(2-aminoethyl)-1,3-propanediamine (AEPD), and3,3′-Diamino-N,N-dimethyldipropylammonium bromide.

[0205] Monomers can also be hydrophobic, hydrophilic or amphipathic.Monomers can also be intercalating agents such as acridine, thiazoleorgange, or ethidium bromide.

[0206] Other Components of the Monomers and Polymers: The polymers haveother groups that increase their utility. These groups can beincorporated into monomers prior to polymer formation or attached to thepolymer after its formation. These groups include: Targeting Groups—suchgroups are used for targeting the polymer-nucleic acid complexes tospecific cells or tissues. Examples of such targeting agents includeagents that target to the asialoglycoprotein receptor by usingasiologlycoproteins or galactose residues. Other proteins such asinsulin, EGF, or transferrin can be used for targeting. Protein refersto a molecule made up of 2 or more amino acid residues connected one toanother as in a polypeptide. The amino acids may be naturally occurringor synthetic. Peptides that include the RGD sequence can be used totarget many cells. Chemical groups that react with thiol, sulfhydryl, ordisulfide groups on cells can also be used to target many types ofcells. Folate and other vitamins can also be used for targeting. Othertargeting groups include molecules that interact with membranes such asfatty acids, cholesterol, dansyl compounds, and amphotericinderivatives.

[0207] After interaction of the supramolecular complexes with the cell,other targeting groups can be used to increase the delivery of the drugor nucleic acid to certain parts of the cell. For example, agents can beused to disrupt endosomes and a nuclear localizing signal (NLS) can beused to target the nucleus.

[0208] A variety of ligands have been used to target drugs and genes tocells and to specific cellular receptors. The ligand may seek a targetwithin the cell membrane, on the cell membrane or near a cell. Bindingof ligands to receptors typically initiates endocytosis. Ligands couldalso be used for DNA delivery that bind to receptors that are notendocytosed. For example peptides containing RGD peptide sequence thatbind integrin receptor could be used. In addition viral proteins couldbe used to bind the complex to cells. Lipids and steroids could be usedto directly insert a complex into cellular membranes.

[0209] The polymers can also contain cleavable groups within themselves.When attached to the targeting group, cleavage leads to reduceinteraction between the complex and the receptor for the targetinggroup. Cleavable groups include but are not restricted to disulfidebonds, diols, diazo bonds, ester bonds, sulfone bonds, acetals, ketals,enol ethers, enol esters, enamines and imines.

[0210] Polyelectrolyte

[0211] A polyelectrolyte, or polyion, is a polymer possessing charge,i.e. the polymer contains a group (or groups) that has either gained orlost one or more electrons. A polycation is a polyelectrolyte possessingnet positive charge, for example poly-L-lysine hydrobromide. Thepolycation can contain monomer units that are charge positive, chargeneutral, or charge negative, however, the net charge of the polymer mustbe positive. A polycation also can mean a non-polymeric molecule thatcontains two or more positive charges. A polyanion is a polyelectrolytecontaining a net negative charge. The polyanion can contain monomerunits that are charge negative, charge neutral, or charge positive,however, the net charge on the polymer must be negative. A polyanion canalso mean a non-polymeric molecule that contains two or more negativecharges. The term polyelectrolyte includes polycation, polyanion,zwitterionic polymers, and neutral polymers. The term zwitterionicrefers to the product (salt) of the reaction between an acidic group anda basic group that are part of the same molecule.

[0212] Chelator

[0213] A chelator is a polydentate ligand, a molecule that can occupymore than one site in the coordination sphere of an ion, particularly ametal ion, primary amine, or single proton. Examples of chelatorsinclude crown ethers, cryptates, and non-cyclic polydentate molecules. Acrown ether is a cyclic polyether containing (—X—(CR1-2)n)m units, wheren=1-3 and m=3-8. The X and CR1-2 moieties can be substituted, or at adifferent oxidation states. X can be oxygen, nitrogen, or sulfur,carbon, phosphorous or any combination thereof. R can be H, C, O, S, N,P. A subset of crown ethers described as a cryptate contain a second(—X—(CR1-2)n)z strand where z=3-8. The beginning X atom of the strand isan X atom in the (—X—(CR1-2)n)m unit, and the terminal CH2 of the newstrand is bonded to a second X atom in the (—X—(CR1-2)n)m unit.Non-cyclic polydentate molecules containing (—X—(CR1-2)n)m unit(s),where n=1-4 and m=1-8. The X and CR1-2 moieties can be substituted, orat a different oxidation states. X can be oxygen, nitrogen, or sulfur,carbon, phosphorous or any combination thereof.

[0214] Polychelator

[0215] A polychelator is a polymer associated with a plurality ofchelators by an ionic or covalent bond and can include a spacer. Thepolymer can be cationic, anionic, zwitterionic, neutral, or contain anycombination of cationic, anionic, zwitterionic, or neutral groups with anet charge being cationic, anionic or neutral, and may contain stericstabilizers, peptides, proteins, signals, or amphipathic compound forthe formation of micellar, reverse micellar, or unilamellar structures.Preferably the amphipathic compound can have a hydrophilic segment thatis cationic, anionic, or zwitterionic, and can contain polymerizablegroups, and a hydrophobic segment that can contain a polymerizablegroup.

[0216] Steric Stabilizer

[0217] A steric stabilizer is a long chain hydrophilic group thatprevents aggregation of final polymer by sterically hindering particleto particle electrostatic interactions. Examples include: alkyl groups,PEG chains, polysaccharides, hydrogen molecules, alkyl amines.Electrostatic interactions are the non-covalent association of two ormore substances due to attractive forces between positive and negativecharges.

[0218] Buffers

[0219] Buffers are made from a weak acid or weak base and their salts.Buffer solutions resist changes in pH when additional acid or base isadded to the solution.

[0220] Biological, Chemical, or Biochemical Reactions

[0221] Biological, chemical, or biochemical reactions involve theformation or cleavage of ionic and/or covalent bonds.

[0222] Reactive

[0223] A compound is reactive if it is capable of forming either anionic or a covalent bond with another compound. The portions of reactivecompounds that are capable of forming covalent bonds are referred to asreactive functional groups.

[0224] Lipids

[0225] Lipids are compounds that are insoluble in water but soluble inorganic solvent which have the general structure composed of twodistinct hydrophobic sections, that is two separate sections ofuninterrupted carbon-carbon bonds. The two hydrophobic sections areconnected through a linkage that contains at least one heteroatom, thatis an atom that is not carbon (e.g. nitrogen, oxygen, silicon, andsulfur). Examples include esters and amides of fatty acids and includethe glycerides (1,2-dioleoylglycerol (DOG)), glycolipids, phospholipids(dioleoylphosphatidylethanolamine (DOPE)).

[0226] Hydrocarbon

[0227] Hydrocarbon means containing carbon and hydrogen atoms; andhalohydrocarbon means containing carbon, halogen (F, Cl, Br, I), andhydrogen atoms.

[0228] Alkyl, Alkene, Alkyne, Aryl

[0229] Alkyl means any sp³-hybridized carbon-containing group; alkenylmeans containing two or more sp² hybridized carbon atoms; aklkynyl meanscontaining two or more sp hybridized carbon atoms; aralkyl meanscontaining one or more aromatic ring(s) in addition containing sp³hybridized carbon atoms; aralkenyl means containing one or more aromaticring(s) in addition to containing two or more sp hybridized carbonatoms; aralkynyl means containing one or more aromatic ring(s) inaddition to containing two or more sp hybridized carbon atoms; steroidincludes natural and unnatural steroids and steroid derivatives.

[0230] Steroid

[0231] A steroid derivative means a sterol, a sterol in which thehydroxyl moiety has been modified (for example, acylated), or a steroidhormone, or an analog thereof. The modification can include spacergroups, linkers, or reactive groups.

[0232] Carbohydrate

[0233] Carbohydrates include natural and unnatural sugars (for exampleglucose), and sugar derivatives (a sugar derivative means a system inwhich one or more of the hydroxyl groups on the sugar moiety has beenmodified (for example, but not limited to, acylated), or a system inwhich one or more of the hydroxyl groups is not present).

[0234] Polyoxyethylene

[0235] Polyoxyethylene means a polymer having ethylene oxide units(—(CH₂CH₂O)_(n)—, where n=2-3000).

[0236] Compound

[0237] A compound is a material made up of two or more elements.

[0238] Electron Withdrawing and Donating Groups

[0239] Electron withdrawing group is any chemical group or atom composedof electronegative atom(s), that is atoms that tend to attractelectrons. Electron donating group is any chemical group or atomcomposed of electropositive atom(s), that is atoms that tend to attractelectrons.

[0240] Resonance Stabilization

[0241] Resonance stabilization is the ability to distribute charge onmultiple atoms through pi bonds. The inductive effective, in a molecule,is a shift of electron density due to the polarization of a bond by anearby electronegative or electropositive atom.

[0242] Sterics

[0243] Steric hindrance, or sterics, is the prevention or retardation ofa chemical reaction because of neighboring groups on the same molecule.

[0244] Activated Carboxylate

[0245] An activated carboxylate is a carboxylic acid derivative thatreacts with nucleophiles to form a new covalent bond. Nucleophilesinclude nitrogen, oxygen and sulfur-containing compounds to produceureas, amides, carbonates, carbamates, esters, and thioesters. Thecarboxylic acid may be activated by various agents includingcarbodiimides, carbonates, phosphoniums, and uroniums to produceactivated carboxylates acyl ureas, acylphosphonates, acid anhydrides,and carbonates. Activation of carboxylic acid may be used in conjunctionwith hydroxy and amine-containing compounds to produce activatedcarboxylates N-hydroxysuccinimide esters, hydroxybenzotriazole esters,N-hydroxy-5-norbornene-endo-2,3-dicarboximide esters, p-nitrophenylesters, pentafluorophenyl esters, 4-dimethylaminopyridinium amides, andacyl imidazoles.

[0246] Nucleophile

[0247] A nucleophile is a species possessing one or more electron-richsites, such as an unshared pair of electrons, the negative end of apolar bond, or pi electrons.

[0248] Cleavage and Bond Breakage

[0249] Cleavage, or bond breakage is the loss of a covalent bond betweentwo atoms. Cleavable means that a bond is capable of being cleaved.

[0250] Substituted Group or Substitution

[0251] A substituted group or a substitution refers to chemical groupthat is placed onto a parent system instead of a hydrogen atom. For thecompound methylbenzene (toluene), the methyl group is a substitutedgroup, or substitution on the parent system benzene. The methyl groupson 2,3-dimethylmaleic anhydride are substituted groups, or substitutionson the parent compound (or system) maleic anhydride.

[0252] Primary and Secondary Amine

[0253] A primary amine is a nitrogen-containing compound that is derivedby monosubstitution of ammonia (NH₃) by a carbon-containing group. Aprimary amine is a nitrogen-containing compound that is derived bydisubstitution of ammonia (NH₃) by a carbon-containing group.

[0254] Preferred Embodiments

[0255] The following description provides exemplary embodiments of thesystems, compositions, and methods of the present invention. Theseembodiments include a variety of systems that have been demonstrated aseffective delivery systems both in vitro and in vivo. The invention isnot limited to these particular embodiments. The following topics arediscussed in turn: I) Labile, pH-labile, Very pH-labile Bonds, andExtremely pH-Labile Bonds II) Polymers with pH-Labile Bonds, III)Polymers Containing Several Membrane Active Compounds, IV) MembraneActive Compounds Containing Labile Bonds, V) Mixtures of Membrane ActiveCompounds and Labile Compounds, VI) Biologically active compoundsContaining Very pH-Labile Bonds, and VII) pH-Labile AmphipathicCompounds

[0256] I. Labile, pH-Labile Bonds, Very pH-Labile, and ExtremelypH-Labile Bonds

[0257] A) Labile Bonds

[0258] In one embodiment, disulfide bonds are used in a variety ofmolecules, and polymers that include peptides, lipids, liposomes.

[0259] B) pH-Labile

[0260] In one embodiment, ketals that are labile in acidic environments(pH less than 7, greater than 4) to form a diol and a ketone are used ina variety of molecules and polymers that include peptides, lipids, andliposomes.

[0261] In one embodiment, acetals that are labile in acidic environments(pH less than 7, greater than 4) to form a diol and an aldehyde are usedin a variety of molecules and polymers that include peptides, lipids,and liposomes.

[0262] In one embodiment, imines or iminiums that are labile in acidicenvironments (pH less than 7, greater than 4) to form an amine and analdehyde or a ketone are used in a variety of molecules and polymersthat include peptides, lipids, and liposomes.

[0263] The present invention additionally provides for the use ofpolymers containing silicon-oxygen-carbon linkages (either in the mainchain of the polymer or in a side chain of the polymer) that are labileunder acidic conditions. Organosilanes have long been utilized as oxygenprotecting groups in organic synthesis due to both the ease inpreparation (of the silicon-oxygen-carbon linkage) and the facileremoval of the protecting group under acidic conditions. For example,silyl ethers and silylenolethers, both posses such a linkage.Silicon-oxygen-carbon linkages are susceptible to hydrolysis underacidic conditions forming silanols and an alcohol (or enol). Thesubstitution on both the silicon atom and the alcohol carbon can affectthe rate of hydrolysis due to steric and electronic effects. This allowsfor the possibility of tuning the rate of hydrolysis of thesilicon-oxygen-carbon linkage by changing the substitution on either theorganosilane, the alcohol, or both the organosilane and alcohol tofacilitate the desired affect. In addition, charged or reactive groups,such as amines or carboxylate, may be linked to the silicon atom, whichconfers the labile compound with charge and/or reactivity.

[0264] The present invention additionally provides for the use ofpolymers containing silicon-nitrogen (silazanes) linkages (either in themain chain of the polymer or in a side chain of the polymer) that aresusceptible to hydrolysis. Hydrolysis of a silazane leads to theformation of a silanol and an amine. Silazanes are inherently moresusceptible to hydrolysis than is the silicon-oxygen-carbon linkage,however, the rate of hydrolysis is increased under acidic conditions.The substitution on both the silicon atom and the amine can affect therate of hydrolysis due to steric and electronic effects. This allows forthe possibility of tuning the rate of hydrolysis of the silizane bychanging the substitution on either the silicon or the amine tofacilitate the desired affect.

[0265] The present invention additionally provides for the use ofpolymers containing silicon-carbon linkages (either in the main chain ofthe polymer or in a side chain of the polymer) that are susceptible tohydrolysis. For example, arylsilanes, vinylsilanes, and allylsilanes allposses a carbon-silicon bond that is susceptible to hydrolysis.

[0266] C) Very pH-Labile Bonds

[0267] To construct labile molecules, one may construct the moleculewith bonds that are inherently labile such as disulfide bonds, diols,diazo bonds, ester bonds, sulfone bonds, acetals, ketals, enol ethers,enol esters, imines, imminiums, and enamines. In addition, one mayconstruct a polymer in such a way as to put reactive groups, i.e.electrophiles and nucleophiles, in close proximity so that reactionbetween the function groups is more rapid than if the reactive groupsare not in close proximity. Examples include having carboxylic acidderivatives (acids, esters, amides) and alcohols, thiols, carboxylicacids or amines in the same molecule reacting together to make esters,thiol esters, acid anhydrides or amides.

[0268] An example of the construction of labile molecules containinglabile bonds is the use of the acid labile enol ether bond. The enolether is an ether, a molecule containing a —C—O—C— linkage, in which oneof the carbons bonded to oxygen is sp2 hybridized and bonded to anothercarbon, i.e. an enol. Enols are unstable and rapidly convert to thecarbonyl, i.e. the ketone or aldehyde. Enol ethers are stable, relativeto enols, but under acidic aqueous conditions convert to alcohol andketone or aldehyde. Depending on the structures of the carbonyl compoundformed and the alcohol release, enol hydrolysis can be very pH-labile.In general, hydrolysis to form ketones is much faster than the rate ofconversion to aldehydes. For example the rate of hydrolysis of ethylisopropenyl ether to form ethanol and acetone is ca. 3600 times fasterthan the hydrolysis of ethyl trans-propenyl ether to form ethanol andpropanal.

[0269] Cleavage of an Enol Ether.

[0270] There are two relatively facile methods for the synthesis ofketone-generation enol ether, although the generation of enol ethers isnot limited to these methods and one skilled in the art may find more.One method, metal-liquid ammonia reduction of aromatic compounds, suchas phenol ethers, results in the reduction of one carbon-carbon doublebond to produce a diene (Birch A. J. J. Chem. Soc. 1946, 593). Anothermethod is the elimination of β-halogen ethers (where chloride, fluoride,bromide, and iodide are halogens) under basic conditions.

[0271] Two synthetic strategies for the generation of enol ethers

[0272] An advantage of these methods is that the labile enol ether isproduced from relatively stable ethers. This stability of startingmaterial enables one to construct the labile molecule under conditionswhere it is not labile and then produce the labile enol ether linkage.Using suitable β-haloethers, both methods produce enol ethers thathydrolyze into ketones, which enable one to construct very pH-labilebonds. For example analogs of ethyl isopropenyl ether, which may besynthesized from P-haloethers, have half-lives of roughly 2 minutes atpH 5 (Kresge, A. J.; Sagatys, D. S.; Chen, H. L. J. Am. Chem. Soc. 1977,99, 7228). A facile method for the production of a polymer containingisoproprenyl ether is the elimination of polyepichlorohydrin under basicconditions (Nishikubo, T., Iiazawa, T., Sugarwara, Y., and Shimokawa, T.J. Polym. Sci., Polym Chem. Ed. 1986, 24, 1097.) It has been shown(Perez, M., Ronda, J. C., Reina, J. A., Serra, A. Polymer 1998, 39,3885.) that reaction of epichlorohydrin with phenolate salts is acompetition between substitution, to form the phenol ether, andelimination to form the enol ether. To, illustrate the use ofelimination of β-haloethers to construct enol ether-containing polyions,we reacted polyepichlorohydrin with the tetrabutylammonium disalt ofpara-hydroxyphenylacetic acid. The product was a polyanion, due to thesubstitution reaction, which had enol ether functional groups. Thispolyanion's ability to from complexes with polyallylamine was lost uponacidification. In addition this enol either is very pH-labile:measurement of the rate of hydrolysis of the enol ether group by UVspectroscopy revealed a hydrolysis with a half-life of 37 minutes at pH5.

[0273] Analogs of ethyl cyclohexenyl ether, which may be synthesizedfrom phenol ethers, have half-lives of roughly 14 minutes at pH 5(Kresge, A. J.; Sagatys, D. S.; Chen, H. L. J. Am. Chem. Soc. 1977, 99,7228). To illustrate this approach to construct enol ethers, wesynthesized glycolic acid ethoxylate(4 units)4-tert-buty-1,4-cyclohexadiene ether by metal-liquid ammonia reductionof glycolic acid ethoxylate(4 units) 4-tert-buty-phenyl ether, which isa phenol ether. The hydrolysis of this enol ether is very acid labile.The half-life of the hydrolysis of this enol ether -containingsurfactant was 40 minutes at pH 5.

[0274] D. Extremely pH-Labile Bonds

[0275] An illustrative embodiment of the present invention, in whichproximity of reactive groups confers lability, is shown by theconversion of amine to amides with anhydrides. Reaction of an amine withan anhydride results in the formation of an amide and a carboxylic acid.As is the case with all chemical reactions, this coupling of amine andanhydride is, in theory, reversible. However, as is the case for manychemical reactions, the reverse reaction (between a carboxylic acid andamide to form an anhydride and amine) is so unfavorable that thereaction between an amine and an anhydride is considered irreversible.Exceptions to this irreversibility are observed when the anhydride is acyclic anhydride such that the formed amide and acid are in the samemolecule, an amide acid. Placement of both reactive groups (amide andcarboxylic acid) in the same molecule accelerates their reaction suchthat amine-anhydride reactivity becomes functionally reversible. Forexample, the product of succinic anhydride and a primary amine, asuccinamic acid, reverse back to amine and anhydride 10,000 times fasterthan the products between noncyclic anhydride and a primary amine. Inparticular, the product of primary amines with maleic anhydride andmaleic anhydride derivatives, maleamic acids, revert back to amine andanhydride with amazing speed, 1×10⁹ to 1×10¹³ times faster than itsnoncyclic analogues (Kirby, A J. J. Adv. Phys. Org Chem. 1980, 17, 183)

[0276] Reaction of an Amine and an Anhydride to Form an Amide Acid.

[0277] The amide acid that converts to amine and anhydride is theprotonated acid, not the deprotonated carboxylate. For this reason,cleavage of the amide acid to form amine and anhydride is pH-dependent.This pH-dependent reactivity can be exploited to form reversiblepH-sensitive linkers. Linkers, or spacer molecules, are used toconjugate passenger molecules and carrier molecules, which increase thetransport and delivery of passenger molecules. Specifically,cis-aconitic acid is used as such a pH-sensitive linker molecule. Theγ-carboxylate is first coupled to a carrier molecule, a molecule thatassists in delivery such as an interaction modifier or a targetingligand. In a second step, either the α or β carboxylate is coupled to apassenger molecule, such as a biologically active compound, to form apH-sensitive coupling of passenger and carrier molecules. An estimationof the kinetics of cleavage between passenger and carrier reveals thatat pH 5 the half-life of cleavage is between 8 and 24 hours (Blattler,W. A.; Kuenzi, B. S.; Lambert, J. M.; Senter, P. D. Biochemistry, 1985,24, 1517-1524).

[0278] Structures of Cis-Aconitic Anhydride and Maleic Anhydride.

[0279] The pH at which cleavage occurs is controlled by the addition ofchemical constituents to the labile moiety. The rate of conversion ofmaleamic acids to amines and maleic anhydrides is strongly dependent onsubstitution (R₂ and R₃) of the maleic anhydride system. When R₂ ismethyl (from citraconic anhydride and similar in substitution tocis-aconitic anhydride) the rate of conversion is 50-fold higher thanwhen R₂ and R₃ are hydrogen (derived from maleic anhydride). When thereare alkyl substitutions at both R₂ and R₃ (e.g.,2,3-dimethylmaleicanhydride) the rate increase is dramatic, 10000-foldfaster than maleic anhydride. Indeed, modification of the polycationpoly-L-lysine with 2,3-dimethylmaleic anhydride to form the polyanionic2,3-dimethylmaleamic poly-L-lysine, followed by incubation at acidic pHresulted in loss of 2,3-dimethylmaleic and return of the polycationpoly-L-lysine. The half-life of this conversion was between 4 and 10minutes at pH 5. This shows that conversion of 2,3-dimethylmaleamicacids (derived from the reaction between 2,3-dimethylmaleic anhydrideand amines at basic pH), to amines and 2,3-dimethylmaleic anhydride atacidic pH is extremely labile. It is postulated that this increase inrate for 2,3-dimethylmaleamic acids is due to the steric interactionsbetween the two methyl groups which increases the interaction betweenamide and carboxylate and thereby increases the rate of conversion toamine and anhydride. Therefore, it is anticipated that if R₂ and R₃ aregroups larger than hydrogen, which includes any conceivable group, therate of amide-acid conversion to amine and anhydride will be faster thanif R₂ and/or R₃ are hydrogen. One would expect that 2,3-diethylmaleamicacids to cleave faster than ethylmaleamic acids and so forth. Inaddition, we synthesized 2-propionic-3-methylmaleic anhydride and foundthat the rate of 2-propionic-3-methylmaleamic acid cleavage was the sameas that for 2,3-dimethylmaleamic acids.

[0280] Another method for the production of rapidly cleaved pH-sensitivederivatives of maleic anhydride is to react the anhydride with analcohol or thiol to form an acid ester or acid thioester.

[0281] II. Polymers with pH-Labile Bonds

[0282] Polymers with labile bonds may have the following generalizedstructures: A-B-A where A is a monomer and B is a pH-labile linkage,A-B—C where A is a monomer and B is a pH-labile linkage and C is aninteraction modifier. The modifying group may confer the polymer with avarieties of new characteristics such as a change in charge (e.g.cationic, anionic), cell targeting capabilities (e.g. nuclearlocalization signals), hydrophilicity (e.g. polyethyleneglycol,saccharides, and polysaccharides)i and hydrophobicity (e.g. lipids anddetergents). The labile group may be added to the polymer during polymersynthesis or the labile group may be added to the polymer afterpolymerization has occurred.

[0283] The present invention provides a wide variety of polymers withlabile groups that find use in the delivery systems of the presentinvention. The labile groups are selected such that they undergo achemical transformation (e.g., cleavage) in physiological conditions,that is, when introduced into a specific, inherent intra orextracellular environment (e.g., the lower pH conditions of an endosome,or the extracellular environment of a cancerous tumor). In addition, thechemical transformation may also be initiated by the addition of acompound. The conditions under which a labile group will undergotransformation can be controlled by altering the chemical constituentsof the molecule containing the labile group. For example, addition ofparticular chemical moieties (e.g., electron acceptors or donors) nearthe labile group can effect the particular conditions (e.g., pH) underwhich chemical transformation will occur. The present invention providesassays for the selection of the desired properties of the labile groupfor any desired application. A labile group is selected based upon itshalf-life and is included in a polymer. The polymer is then complexedwith the biologically active compounds and an in vitro or in vivo assayis used to determine whether the compound's activity is affected.

[0284] A. pH-Labile Linkages Within pH-Labile Polymers

[0285] The pH-labile bond may either be in the main-chain or in the sidechain. If the pH-labile bond occurs in the main chain, then cleavage ofthe labile bond results in a decrease in polymer length. If thepH-labile bond occurs in the side chain, then cleavage of the labilebond results in loss of side chain atoms from the polymer.

[0286] An example of a pH-labile bond in the side chain of a polymer is2,3-dimethylmaleamic poly-L-lysine, which is formed by the reaction ofpoly-L-lysine with 2,3-dimethylmaleic anhydride under basic conditions.The modification of the poly-L-lysine is in the side chain andconversion of the 2,3-dimethylmaleamic poly-L-lysine to poly-L-lysineand 2,3-dimethylmaleic anhydride under acid conditions does not resultin a cleavage of the polymer main, but in a cleavage of the side chain.

[0287] An example of a silicon-oxygen-carbon pH-labile bond in the sidechain of the polymer is the polymer formed from the reaction ofpoly-L-serine and 3-aminopropyltrimethoxysilane in DMF. The ratio of3-aminopropyl-trimethoxysilane per serine monomer units may be changedresulting in differing amounts of silylether formation. Hydrolysis ofthe polymer under acidic conditions regenerates the poly-L-serine and asilanol.

[0288] An example of a pH-labile bond in the main chain of the polymeris di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene:1,4-bis(3-aminopropyl)piperazinecopolymer (1:1) (MC208) prepared from the reaction ofdi-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene and: 1,4-bis(3-aminopropyl)piperazine.The resulting polymer (containing imines) can be reduced in the presenceof NaCNBH₃ to afford the secondary amine containing copolymer (MC301)which retains the pH-lability of the parent polymer, through ketalfunctional groups. Both polymers contain a substituted 1,3-dioxolanering system, ketal, which upon exposure to acidic environmentshydrolyzes to a ketone and diol.

[0289] B. Polymerization Processes to Form the pH-Labile Polymers

[0290] There are a number of polymerization processes that can beutilized with the present invention. For example, the polymerization canbe chain or step. This classification description is more often usedthat the previous terminology of addition and condensation polymer.“Most step-reaction polymerizations are condensation processes and mostchain-reaction polymerizations are addition processes” (M. P. StevensPolymer Chemistry: An Introduction New York Oxford University Press1990). Template polymerization can be used to form polymers fromdaughter polymers.

[0291] 1. Step Polymerization: In step polymerization, thepolymerization occurs in a stepwise fashion. Polymer growth occurs byreaction between monomers, oligomers and polymers. No initiator isneeded since there is the same reaction throughout and there is notermination step so that the end groups are still reactive. Thepolymerization rate decreases as the functional groups are consumed.

[0292] Typically, step polymerization is done either of two differentways. One way, the monomer has both reactive functional groups (A and B)in the same molecule so that A-B yields -[A-B]-Or the other approach isto have two bifunctional monomers. A-A+B—B yields -[A-A-B—B]—Generally,these reactions can involve acylation or alkylation. Acylation isdefined as the introduction of an acyl group (—COR) onto a molecule.Alkylation is defined as the introduction of an alkyl group onto amolecule.

[0293] If functional group A is an amine then B can include, but is notlimited to, an isothiocyanate, isocyanate, acyl azide,N-hydroxysuccinimide, sulfonyl chloride, aldehyde (includingformaldehyde and glutaraldehyde), ketone, epoxide, carbonate,imidoester, carboxylate activated with a carbodiimide, alkylphosphate,arylhalides (difluoro-dinitrobenzene), anhydride, or acid halide,p-nitrophenyl ester, o-nitrophenyl ester, pentachlorophenyl ester,pentafluorophenyl ester, carbonyl imidazole, carbonyl pyridinium, orcarbonyl dimethylaminopyridinium. In other terms when function A is anamine then function B can be acylating or alkylating agent or aminationagent.

[0294] If functional group A is a thiol, sulfhydryl, then function B caninclude, but is not limited to, an iodoacetyl derivative, maleimide,aziridine derivative, acryloyl derivative, fluorobenzene derivatives, ordisulfide derivative (such as a pyridyl disulfide or5-thio-2-nitrobenzoic acid {TNB} derivatives).

[0295] If functional group A is carboxylate then function B can include,but is not limited to, a diazoacetate or an amine in which acarbodiimide is used. Other additives may be utilized such ascarbonyldiimidazole, dimethylamino pyridine (DMAP), N-hydroxysuccinimideor alcohol using carbodiimide and DMAP.

[0296] If functional group A is an hydroxyl then function B can include,but is not limited to, an epoxide, oxirane, or an amine in whichcarbonyldiimidazole or N,N′-disuccinimidyl carbonate, orN-hydroxysuccinimidyl chloroformate or other chloroformates are used.

[0297] If functional group A is an aldehyde or ketone then function Bcan include, but is not limited to, an hydrazine, hydrazide derivative,amine (to form a imine or iminium that may or may not be reduced byreducing agents such as NaCNBH₃) or hydroxyl compound to form a ketal oracetal.

[0298] Yet another approach is to have one bifunctional monomer so thatA-A plus another agent yields -[A-A]-. If function A is a thiol,sulfhydryl, group then it can be converted to disulfide bonds byoxidizing agents such as iodine (12) or NaIO₄ (sodium periodate), oroxygen (O₂). Function A can also be an amine that is converted to athiol, sulfhydryl, group by reaction with 2-Iminothiolate (Traut'sreagent) which then undergoes oxidation and disulfide formation.Disulfide derivatives (such as a pyridyl disulfide or5-thio-2-nitrobenzoic acid {TNB} derivatives) can also be used tocatalyze disulfide bond formation.

[0299] Functional group A or B in any of the above examples could alsobe a photoreactive group such as aryl azide (including halogenated arylazide), diazo, benzophenone, alkyne or diazirine derivative.

[0300] Reactions of the amine, hydroxyl, thiol, sulfhydryl, carboxylategroups yield chemical bonds that are described as amide, amidine,disulfide, ethers, esters, enamine, imine, urea, isothiourea, isourea,sulfonamide, carbamate, alkylamine bond (secondary amine),carbon-nitrogen single bonds in which the carbon contains a hydroxylgroup, thioether, diol, hydrazone, diazo, or sulfone.

[0301] 2. Chain Polymerization: In chain-reaction polymerization, growthof the polymer occurs by successive addition of monomer units to limitednumber of growing chains. The initiation and propagation mechanisms aredifferent and there is usually a chain-terminating step. Thepolymerization rate remains constant until the monomer is depleted.

[0302] Monomers containing (but not limited to) vinyl, acrylate,methacrylate, acrylamide, methacrylamide groups can undergo chainreaction which can be radical, anionic, or cationic. Chainpolymerization can also be accomplished by cycle or ring openingpolymerization. A number of different types of free radical initiatorscould be used that include peroxides, hydroxy peroxides, and azocompounds such as 2,2′-Azobis(-amidinopropane)dihydrochloride (AAP).

[0303] C. Types of Monomers for Incorporation into pH-Labile Polymersand Types of pH-Labile Polymers

[0304] A wide variety of monomers can be used in the polymerizationprocesses. These include positive charged organic monomers such asamines, amine salts, imidine, guanidine, imine, hydroxylamine,hydrazine, heterocycles like imidazole, pyridine, morpholine,pyrimidine, or pyrene. Polymers from such monomers includes, but are notlimited to such examples as poly-L-lysine, polyethylenimine (linear andbranched), and polyallylamine. The amines could be pH-sensitive in thatthe pKa of the amine is within the physiologic range of 4 to 8. SpecificpH-sensitive amines include spermine, spermidine,N,N′-bis(2-aminoethyl)-1,3-propanediamine (AEPD), and3,3′-Diamino-N,N-dimethyldipropylammonium bromide.

[0305] In addition negatively charged monomers such as sulfates,sulfonates, carboxylates, and phosphates may be used to generatedpolyanionic polymers. Examples of these polyanions include, but are notlimited to, nucleic acids, polysulfonylstyrene, and heparin sulfate.Also, amine-containing polycations may be converted to polyanions byreaction with cyclic anhydrides such as succinic anhydride and glutaricanhydride to form glutarylated and succinylated polymers which arepolyanionic. Examples of these polyanions include, but are not limitedto, succinylated and glutarylated poly-L-lysine, and succinylated andglutarylated polyallylamine.

[0306] Monomers can also be hydrophobic, hydrophilic or amphipathic.

[0307] Monomers can also be intercalating agents such as acridine,thiazole organge, or ethidium bromide. Monomers can also containchemical moieties that can be modified before or after thepolymerization including (but not limited to) amines (primary,secondary, and tertiary), amides, carboxylic acid, ester, hydroxyl,hydrazine, alkyl halide, aldehyde, and ketone.

[0308] The pH-labile polymer can be a polyion, polycation, polyanion,zwitterionic polymers, and neutral polymers. It can also contain achelator and be a polychelator.

[0309] D. Other Components of the Monomers and Polymers

[0310] The polymers may include other groups that increase theirutility. These groups can be incorporated into monomers prior to polymerformation or attached to the polymer after its formation. These groupsinclude, but are not limited to: targeting groups and signals (e.g, cellreceptor, nuclear targeting signals), membrane active compounds,reporter or marker molecules, spacers, steric stabilizers, chelators,polycations, polyanions, and polymers.

[0311] III. Polymers Containing Several Membrane Active Compounds

[0312] The present invention specifies polymers containing more than twomembrane active compounds. In one embodiment, the membrane activecompounds are grafted onto a preformed polymer to form a comb-typepolymer. For example, both the membrane active peptides melittin and KL₃contain only one carboxylate, which is at the carboxy terminus.Therefore, activation of the peptides with carboxy-activating agentssuch as carbodiimides will react with only one group. If this activationis done in the presence of an excess of an amine, then one may obtainselective amide formation. In particular, if the activation is done inthe presence of a polyamine, one would obtain selective coupling of thepeptide to the polyamine. This method of coupling of a membrane activepeptide to a polyamine was accomplished for the coupling of peptides KL₃and melittin to polyamines polyallylamine and poly-L-lysine. In eachcase, the membrane activity, as judged by hemolysis, was retained and,in case of KL₃, was improved after attachment to the polycation.

[0313] In another embodiment, the membrane active compounds areincorporated into the polymer by chain or step polymerization processes.For example, an acryloyl group at the N-terminus of a peptide allows oneto form a polyacrylamide polymer with peptide side chains(O'Brien-Simpson, N. M., Ede, N. J., Brown, L. E., Swan, J., Jackson, D.C J. Am. Chem. Soc. 1997, 119, 1183). N-acryloyl KL3 was synthesized andpolymerized and found to retain the activity of monomeric KL3, but wasable to form particles with DNA.

[0314] IV. Membrane Active Compounds Containing Labile Bonds

[0315] The invention specifies compounds that are of the generalstructure: A-B—C wherein A is a membrane active compound, B is a labilelinkage, and C is a compound that inhibits the membrane activity ofcompound A. A membrane active compound is defined within the DefinitionsSection and includes membrane active peptides.

[0316] The term labile linkage is defined above and includes pH-labilebonds such as, acetals, ketals, enol ethers, enol esters, enamines, andimines. It also includes extremely pH-labile bonds such as2,3-disubstituted maleamic acids and very pH-labile bonds such as enolethers.

[0317] Preferred embodiments include 2,3-dimethylmaleamic-mellitin,2-propionic-3-methylmaleamic melittin, 2-propionic-3-methylmaleamic KL3,and 2,3-dimethylmaleamic-melittin, which are membrane inactive compoundsthat become membrane active under acidic conditions.

[0318] The disulfide linkage (RSSR′) may be used within bifunctionalmolecules. The reversibility of disulfide bond formation makes themuseful tools for the transient attachment of two molecules. Disulfideshave been used to attach a bioactive compound and another compound(Thorpe, P. E. J. Natl. Cancer Inst. 1987, 79, 1101). The disulfide bondis reduced thereby releasing the bioactive compound. Disulfide bonds mayalso be used in the formation of polymers (Kishore, K., Ganesh, K. inAdvances in Polymer Science, Vol. 21, Saegusa, T. Ed., 1993).

[0319] In another embodiment, the invention includes compositionscontaining biologically active compounds and compounds of the generalstructure: A-B—C wherein A is a membrane active compound, B is a labilelinkage, and C is a compound that inhibits the membrane activity ofcompound A. The biologically active compounds include pharmaceuticaldrugs, nucleic acids and genes. In yet another embodiment, thesecompounds that are of the general structure—A-B—C wherein A is amembrane active compound, B is a labile linkage, and C is a compoundthat inhibits the membrane activity of compound A- are used to deliverbiologically active compounds that include pharmaceutical drugs, nucleicacids and genes. In one specific embodiment, these A-B—C compounds areused to deliver nucleic acids and genes to muscle (skeletal, heart,respiratory, striated, and non-striated), liver (hepatocytes), spleen,immune cells, gastrointestinal cells, cells of the nervous system(neurons, glial, and microglial), skin cells (dermis and epidermis),joint and synovial cells, tumor cells, kidney, cells of the immunesystem (dendiritic, T cells, B cells, antigen-presenting cells,macrophages), exocrine cells (pancreas, salivary glands), prostate,adrenal gland, thyroid gland, eye structures (retinal cells), andrespiratory cells (cells of the lung, nose, respiratory tract). Uponcleavage of B, membrane activity is restored to compound A. Thiscleavage occurs in certain tissue, organ, and sub-cellular locationsthat are controlled by the microenvironment of the location and also bythe addition of exogenous agents. Delivery can be accomplished by directintraparenchymal injections (into the parenchyma of a tissue) or byintravascular conditions. Intravascular conditions also includeconditions under which the permeability of the vessel is increased andwhen the injection is leads to increased intravascular pressure.

[0320] V. Mixtures of Membrane Active Compounds and Labile Compounds

[0321] In addition, the invention is a composition of matter thatincludes a membrane active compound and a labile compound. In oneembodiment, the labile compound inhibits the membrane activity of themembrane active compound. Upon chemical modification of the labilecompound, membrane activity is restored to the membrane active compound.This chemical modification occurs in certain tissue, organ, andsub-cellular locations that are controlled by the microenvironment ofthe location and also by the addition of exogenous agents. In oneembodiment the chemical modification involves the cleavage of thepolymer. In one embodiment, the membrane active compound and theinhibitory labile compound are polyions and are of opposite charge. Forexample, the membrane active compound is a polycation and the inhibitorylabile compound is a polyanion, or the membrane active compound is apolyanion and the inhibitory labile compound is a polycation.

[0322] In another embodiment, the invention includes compositionscontaining biologically active compounds, a membrane active compound anda labile compound. Upon chemical modification of the labile compound,membrane activity is restored to the membrane active compound. Thischemical modification occurs in certain tissue, organ, and sub-cellularlocations that are controlled by the microenvironment of the locationand also by the addition of exogenous agents. In one embodiment thechemical modification involves the cleavage of the polymer. In onespecific embodiment, these compositions containing biologically activecompounds, a membrane active compound and a labile compound are used todeliver nucleic acids and genes to muscle (skeletal, heart, respiratory,striated, and non-striated), liver (hepatocytes), spleen, immune cells,gastrointestinal cells, cells of the nervous system (neurons, glial, andmicroglial), skin cells (dermis and epidermis), joint and synovialcells, tumor cells, kidney, cells of the immune system (dendiritic, Tcells, B cells, antigen-presenting cells, macrophages), exocrine cells(pancreas, salivary glands), prostate, adrenal gland, thyroid gland, eyestructures (retinal cells), respiratory cells (cells of the lung, nose,respiratory tract), and endothelial cells.

[0323] VI. Biologically Active Compounds Containing Very and/orExtremely pH-Labile Bonds

[0324] The invention specifies compounds of the following generalstructure: A-B—C wherein A is a biologically active compound such aspharmaceuticals, drugs, proteins, peptides, hormones, cytokines, enzymesand nucleic acids such as anti-sense, ribozyme, recombining nucleicacids, and expressed genes; B is a labile linkage that contains apH-labile bond such as amides of 2,3-dimethylmaleamic acid, enol ethers,enol esters, silyl ethers, and silyl enol ethers; and C is a compound.In one embodiment C is a compound that modifies the activity, function,delivery, transport, shelf-life, pharmacokinetics, blood circulationtime in vivo, tissue and organ targetting, and sub-cellular targeting ofthe biologically active compound A. In other embodiments, B is a labilelinkage that contains acetals, ketals, enol ethers, enol esters, amides,imines, imminiums, enamines, silyl ethers, or silyl enol ethers.

[0325] The invention also specifies that the labile linkage B isattached to reactive functional groups on the biologically activecompound A. In yet another embodiment, reactive functional groups areattached to nucleic acids. Specifically, aziridines, quinones, oxiranes,epoxides, nitrogen mustards, sulfur mustards, and halogen andcarbon-containing compounds such as alkylhalides, halo-amines,alpha-halo amides, esters and acids, may be used to modify nucleic acidsand thereby attach reactive functional groups.

[0326] VII. pH-Labile Amphipathic Compounds

[0327] In one specification of the invention, the pH-labile and verypH-labile linkages and bonds are used within amphipathic compounds anddetergents. The pH-labile amphipathic compounds can be incorporated intoliposomes for delivering biologically active compounds and nucleic acidsto cells. The detergents can be used for cleaning purposes and formodifying the solubility of biologically active compounds such asproteins. pH-labile surfactants may be desirable for their reversiblesolubilization of hydrophobic compounds in water and hydrophiliccompounds in organic solvents. For example, surfactants are necessaryfor the purification of membrane proteins; however, it is oftendifficult to separate membrane proteins and surfactants once thepurification is complete. Labile surfactants may also be morebiodegradable and may reverse the formation of unwanted emulsions orfoams.

[0328] For example the surfactant glycolic acid ethoxylate(4 units)4-tert-buty-phenyl ether was converted in the enol-ether-containingpH-labile surfactant glycolic acid ethoxylate(4 units)4-tert-buty-1,4-cyclohexadiene ether by ammonia-metal reduction of thephenyl group. The enol-ether bond links the hyrdrophilic portion of themolecule with the hydrophobic portion of the molecule, therefore,cleavage of the enol ether bond renders the amphiphilic surfactant intotwo separate molecules (one hydrophilic and one hydrophobic). Thehalf-life of enol ether cleavage was 40 minutes at pH 5. In likewisemanner, similar surfactants such as Triton X-100 may be converted intopH-labile surfactants.

[0329] I) Delivery Systems

[0330] In some embodiments of the present invention, the labile group(e.g., ester, amide or thioester acid) is complexed with lipids andliposomes so that in acidic environments the lipids are modified and theliposome becomes disrupted, fusogenic or endosomolytic. For example, thelipid diacylglycerol is reacted with an anhydride to form an ester acid.After acidification in an intracellular vesicle the diacylglycerolreforms and is very lipid bilayer disruptive and fusogenic.

[0331] In preferred embodiments of the present invention the deliverysystems comprise polymers.

[0332] One of the several methods of nucleic acid delivery to the cellsis the use of DNA-polycation complexes. It has been shown that cationicproteins like histones and protamines or synthetic polymers likepolylysine, polyarginine, polyornithine, DEAE dextran, polybrene, andpolyethylenimine may be effective intracellular delivery agents whilesmall polycations like spermine are ineffective.

[0333] In addition to the delivery of polynucleotides, other bioactivemolecules, such as proteins and small molecule drugs, may be deliveredusing a labile connection. Either through a direct modification of thebioactive molecule or through the formation of a complex with themolecule, which is itself labile.

EXAMPLES Example 1

[0334] Synthesis and Characterization of Labile Compounds

[0335] A) Synthesis of 2-propionic-3-methylmaleic anhydride(carboxydimethylmaleic anhydride or C-DM): To a suspension of sodiumhydride (0.58 g, 25 mmol) in 50 mL anhydrous tetrahydrofuran was addedtriethyl-2-phosphonopropionate (7.1 g, 30 mmol). After bubbling ofhydrogen gas stopped, dimethyl-2-oxoglutarate (3.5 g, 20 mmol) in 10 mLanhydrous tetrahydrofuran was added and stirred for 30 minutes. Water,10 mL, was then added and the tetrahydrofuran was removed by rotaryevaporation. The resulting solid and water mixture was extracted with3×50 mL ethyl ether. The ether extractions were combined, dried withmagnesium sulfate, and concentrated to a light yellow oil. The oil waspurified by silica gel chromatography elution with 2:1 ether:hexane toyield 4 gm (82% yield) of pure triester. The 2-propionic-3-methylmaleicanhydride then formed by dissolving of this triester into 50 mL of a50/50 mixture of water and ethanol containing 4.5 g (5 equivalents) ofpotassium hydroxide. This solution was heated to reflux for 1 hour. Theethanol was then removed by rotary evaporation and the solution wasacidified to pH 2 with hydrochloric acid. This aqueous solution was thenextracted with 200 mL ethyl acetate, which was isolated, dried withmagnesium sulfate, and concentrated to a white solid. This solid wasthen recrystallized from dichloromethane and hexane to yield 2 g (80%yield) of 2-propionic-3-methylmaleic anhydride.

[0336] B) Synthesis of 2,3-dioleoyldiaminopropionic ethylenediamineamide: 2,3-diaminopropionic acid (1.4 gm, 10 mmol) anddimethylaminopyridine (1.4 gm 11 mmol) were dissolved in 50 mL of water.To this mixture was added over 5 minutes with rapid stirring oleoylchloride (7.7 mL, 22 mmol) of in 20 mL of tetrahydrofuran. After all ofthe acid chloride had been added, the solution was allowed to stir for30 minutes. The pH of the solution was 4 at the end of the reaction. Thetetrahydrofuran was removed by rotary evaporation. The mixture was thenpartitioned between water and ethyl acetate. The ethyl acetate wasisolated, dried with magnesium sulfate, and concentrated by rotaryevaporation to yield a yellow oil. The 2,3-dioleoyldiaminopropionic acidwas isolated by silica gel chromatography, elution with ethyl ether toelute oleic acid, followed by 10% methanol 90% methylene chloride toelute diamide product, 1.2 g (19% yield). The diamide (1.1 gm, 1.7 mmol)was then dissolved in 25 mL of methylene chloride. To this solution wasadded N-hydroxysuccinimide (0.3 g. 1.5 eq) and dicyclohexylcarbodiimide(0.54 g, 1.5 eq). This mixture was allowed to stir overnight. Thesolution was then filtered through a cellulose plug. To this solutionwas added ethylene diamine (1 gm, 10 eq) and the reaction was allowed toproceed for 2 hours. The solution was then concentrated by rotaryevaporation. The resulting solid was purified by silica gelchromatography elution with 10% ammonia saturated methanol and 90%methylene chloride to yield the triamide product2,3-dioleoyldiaminopropionic ethylenediamine amide (0.1 gm, 9% yield).The triamide product was given the number MC213.

[0337] C) Synthesis of dioleylamideaspartic acid.N-(tert-butoxycarbonyl)-L-aspartic acid (0.5 gm, 2.1 mmol) was dissolvedin 50 mL of acetonitrile. To this solution was addedN-hydroxysuccinimide (0.54 gm, 2.2 eq) and was addeddicyclohexylcarbodiimide (0.54 g, 1.5 eq). This mixture was allowed tostir overnight. The solution was then filtered through a cellulose plug.This solution was then added over 6 hours to a solution containingoleylamine (1.1 g, 2 eq) in 20 mL methylene chloride. After the additionwas complete the solvents were removed by rotary evaporation. Theresulting solid was partitioned between 100 mL ethyl acetate and 100 mLwater. The ethyl acetate fraction was then isolated, dried by sodiumsulfate, and concentrated to yield a white solid. The solid wasdissolved in 10 mL of triflouroacetic acid, 0.25 mL water, and 0.25 mLtriisopropylsilane. After two hours, the triflouroacetic acid wasremoved by rotary evaporation. The product was then isolated by silicagel chromatography using ethyl ether followed by 2% methanol 98%methylene chloride to yield 0.1 gm (10% yield) of puredioleylamideaspartic acid, which was given the number MC303.

[0338] D) Synthesis of2,3-dimethylmaleamic poly-L-lysine: Poly-L-lysine(10 mg 34,000 MW Sigma Chemical ) was dissolved in 1 mL of aqueouspotassium carbonate (100 mM). To this solution was added2,3-dimethylmaleic anhydride (100 mg, 1 mmol) and the solution wasallowed to react for 2 hr. The solution was then dissolved in 5 mL ofaqueous potassium carbonate (100 mM) and dialyzed against 3×2 L waterthat was at pH8 with addition of potassium carbonate. The solution wasthen concentrated by lyophilization to 10 mg/mL of 2,3-dimethylmaleamicpoly-L-lysine.

[0339] E) Synthesis of dimethylmaleamic-melittin anddimethylmaleamic-pardaxin. Solid melittin or pardaxin (100 μg) wasdissolved in 100 μL of anhydrous dimethylformamide containing 1 mg of2,3-dimethylmaleic anhydride and 6 μL of diisopropylethylamine.

[0340] F) Synthesis of dimethylmaleic derivatives (fromalcohol-containing) and dimethylmaleamic derivatives (fromamine-containing) of lipids: To a solution of 1 mg of lipid (either MC213, MC 303, phosphatidylethanolamine dioleoyl (DOPE), or1,2-dioleoylglycerol (DOG)) in chloroform (0.1 mL) is added 10 mg of2,3-dimethylmaleic anhydride and 82 mg of diisopropylethyl amine. Thesolution is allowed to incubate at room temperature for 1 hour beforetesting for activity.

[0341] G) Synthesis of2-propionic-3-methylmaleic derivatives (fromalcohol-containing) and 2-propionic-3-methylmaleamic derivatives (fromamine-containing) of lipids: To a solution of 1 mg of lipid (either MC213, MC 303, phosphatidylethanolamine dioleoyl (DOPE), or1,2-dioleoylglycerol (DOG)) in chloroform (0.1 mL) is added 10 mg of2-propionic-3-methylmaleic anhydride and 82 mg of diisopropylethylamine. The solution is allowed to incubate at room temperature for 1hour before testing for activity.

[0342] H) Synthesis of adducts between peptide and poly-L-lysineadducts: To a solution of poly-L-lysine (10 mg, 0.2 μmol) and peptidesKL₃ or melittin (2 μmol) is added1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (20 μmol).For the peptide KL₃, the reaction is performed in 2 mL of water. For thepeptide melittin, the reaction is performed in a solution of 1 mL waterand 1 mL triflouroethanol. The reaction is allowed to proceed overnightbefore placement into a 12,000 molecular weight cutoff dialysis bag anddialysis against 4×2 liters over 48 hours. The amount of coupled peptideis determined by the absorbance of the tryptophan residue at 280 nm,using an extinction coefficient of 5690 cm⁻¹M⁻¹ (Gill, S. C. and vonHippel, P. H. Analytical Biochemistry (1989) 182, 319-326). Theconjugate of melittin and poly-L-lysine was determined to have 4molecules of melittin per molecule of poly-L-lysine and is referred toas mel-PLL. The conjugate of KL₃ and poly-L-lysine was determined tohave 10 molecules of KL₃ per molecule of poly-L-lysine and is referredto as KL₃-PLL.

[0343] I) Synthesis of adducts between peptide and polyallylamineadducts: To a solution of polyallylamine (10 mg, 0.2 μmol) and peptidesKL₃ or melittin (2 μmol) is added1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (20 μmol).For the peptide KL₃, the reaction is performed in 2 mL of water. For thepeptide melittin, the reaction is performed in a solution of 1 mL waterand 1 mL triflouroethanol. The reaction is allowed to proceed overnightbefore placement into a 12,000 molecular weight cutoff dialysis bag anddialysis against 4×2 liters over 48 hours to remove uncoupled peptide.The amount of coupled peptide is determined by the absorbance of thetryptophan residue at 280 nm, using an extinction coefficient of 5690cm⁻¹M⁻¹ (Gill, S. C. and von Hippel, P. H. Analytical Biochemistry(1989) 182, 319-326). The conjugate melittin and polyallylamine wasdetermined to have 4 molecules of melittin per molecule ofpolyallylamine and is referred to as mel-PAA. The conjugate of KL₃ andpolyallylamine was determined to have 10 molecules of KL₃ per moleculeof polyallylamine and is referred to as KL₃-PAA.

[0344] J) Synthesis of polyethyleneglycol methyl ether2-propionic-3-methylmaleate (CDM-PEG): To a solution of2-propionic-3-methylmaleic anhydride ( 30 mg, 0.16 mmol) in 5 mLmethylene chloride was added oxalyl chloride (200 mg, 10 eq) anddimethylformamide (1 μL). The reaction was allowed to proceed overnightat which time the excess oxalyl chloride and methylene chloride wereremoved by rotary evaporation to yield the acid chloride, a clear oil.The acid chloride was dissolved in 1 mL of methylene chloride. To thissolution was added polyethyleneglycol monomethyl ether, molecular weightaverage of 5,000 (815 mg, 1 eq) and pyridine (20 μL, 1.5 eq) in 10 mL ofmethylene chloride. The solution was then stirred overnight. The solventwas then removed and the resulting solid was dissolved into 8.15 mL ofwater.

[0345] K) General procedure for the reaction of mel-PAA, KL₃-PAA,mel-PLL, and KL₃-PLL with dimethylmaleic anhydride and2-propionic-3-methylmaleic anhydride: Peptide-polycation conjugates (10mg/mL) in water were reacted with a ten-fold weight excess ofdimethylmaleic anhydride and a ten-fold weight excess of potassiumcarbonate. Analysis of the amine content after 30 by addition of peptidesolution to 0.4 mM trinitrobenzene sulfonate and 100 mM borax revealedno detectable amounts of amine.

[0346] L) Synthesis of glycolic acid ethoxylate(4 units)4-tert-buty-1,4-cyclohexadiene ether (an enolether containingdetergent): To a solution of glycolic acid ethoxylate(4 units)4-tert-buty-phenyl ether (100 mg, 0.26 mmol), t-butylalcohol (10 mL),and tetrahydrofuran (10 mL) was condensed liquid anhydrous ammonia (20mL) at −78° C. To this solution was added sodium metal (100 mg, 16 eq).The solution turned dark blue and was stirred for 4 hours during whichtime the blue color remained. The solution was then quenched by theaddition of ammonium chloride (220 mg, 16 eq). The ammonia was allowedto evaporate overnight. The mixture was then partitioned between 10 mLof water and 10 mL ethyl ether. The water layer was isolated and usedfor kinetic studies.

[0347] M) Synthesis ofpoly(oxy-1-para-aceticphenoxymethylethylene-co-oxy-1-methylethylene). Topara-hydroxyphenylacetic acid (0.115 gm, 0.75 mmol) was added a 1 Msolution of tetrabutylammonium hydroxide in methanol. The methanol wasthen removed by rotary evaporation to yield an oil. To this was added 5mL of tetrahydrofuran and polyepichlorohydrin (0.046 gm, 0.6 mg). Thesolution was then heated to 60° C. for 16 hours. The solution was thenplaced into dialysis tubing (12,000 molecular weight cutoff) anddialyzed against 2×1 L of water that was pH 9 with addition of potassiumcarbonate. A portion of this solution was filtered through a 0.2 μmnylon syringe filter, and then lyophilized to determine itsconcentration. This solution was used for particle formation andhydrolysis studies.

[0348] N) Synthesis of L-cystine-1,4-bis(3-aminopropyl)piperazinecopolymer: To a solution of N,N′-Bis(t-BOC)-L-cystine (85 mg, 0.15 mmol)in ethyl acetate (20 mL) was added N,N′-dicyclohexylcarbodiimide (108mg, 0.5 mmol) and N-hydroxysuccinimide (60 mg, 0.5 mmol). After 2 hr,the solution was filtered through a cotton plug and1,4-bis(3-aminopropyl)piperazine (54 μL, 0.25 mmol) was added. Thereaction was allowed to stir at room temperature for 16 h. The ethylacetate was then removed by rotary evaporation and the resulting solidwas dissolved in trifluoroacetic acid (9.5 mL), water (0.5 mL) andtriisopropylsilane (0.5 mL). After 2 h, the trifluoroacetic acid wasremoved by rotary evaporation and the aqueous solution was dialyzed in a15,000 MW cutoff tubing against water (2×21) for 24 h. The solution wasthen removed from dialysis tubing, filtered through 5 μM nylon syringefilter and then dried by lyophilization to yield 30 mg of polymer.

[0349] Synthesis of Acid Labile Monomers:

[0350] O) Synthesis ofDi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (MC 216). To asolution of diacetylbenzene (2.00 g, 12.3 mmol, Aldrich ChemicalCompany) in toluene (30.0 mL), was added glycerol (5.50 g, 59.7 mmol,Acros Chemical Company) followed by p-toluenesulfonic acid monohydrate(782 mg, 4.11 mmol, Aldrich Chemical Company). The reaction mixture washeated at reflux for 5 hrs with the removal of water by azeotropicdistillation in a Dean-Stark trap. The reaction mixture was concentratedunder reduced pressure, and the residue was taken up in Ethyl Acetate.The solution was washed 1×10% NaHCO₃, 3×H₂O, 1× brine, and dried(MgSO₄). Following removal of solvent (aspirator), the residue waspurified by flash chromatography on silica gel (20×150 mm, CH₂Cl₂eluent) to afford 593 mg (16% yield) ofdi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene.

[0351] Molecular ion calculated for C₁₆H₂₂O₆ 310, found m+1/z 311.2; 300MHz NMR (CDCl₃, ppm) δ7.55−7.35 (4H, m) 4.45-3.55 (10H, m) 1.65 (6 H,brs).

[0352] P) Di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene (MC 211): To a solution of succinicsemialdehyde (150 mg, 1.46 mmol, Aldrich Chemical Company) anddi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (150 mg, 480μmol) in CH₂Cl₂ (4 mL) was added dicyclohexylcarbodiimide (340 mg, 1.65mmol, Aldrich Chemical Company) followed by a catalytic amount of4-dimethylaminopyridine. The solution was stirred for 30 min andfiltered. Following removal of solvent (aspirator), the residue waspurified by flash chromatography on silica gel (20×150 mm, CH₂Cl₂eluent) to afford 50 mg (22%) of di-(2-methyl-4-hydroxymethyl(succinicsemialdehyde ester)-1,3-dioxolane)-1,4-benzene. Molecular ion calculatedfor C₂₄H₃₀O₁₀ 478.0 found m+1/z 479.4.

[0353] Q) Di-(2-methyl-4-hydroxymethyl(glyoxilic acidester)-1,3-dioxolane)-1,4-benzene (MC225). To a solution of glyoxylicacid monohydrate (371 mg, 403 μmol, Aldrich Chemical Company) anddi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (500 mg, 161μmol) in dimethylformamide (8 mL) was added dicyclohexylcarbodiimide(863 mg, 419 μmol, Aldrich Chemical Company). The solution was stirredfor 30 min and filtered. Following removal of solvent (aspirator), theresidue was purified by flash chromatography on silica gel (20×150 mm,ethylacetate/Hexanes (1:2.3 eluent) to afford 58 mg (10%) ofdi-(2-methyl-4-hydroxymethyl(glyoxylic acidester)-1,3-dioxolane)-1,4-benzene.

[0354] R) Di-(2-methyl-4-aminomethyl-1,3-dioxolane)-1,4-benzene (MC372).To a solution of 1,4-diacetylbenzene (235 mg, 1.45 mmol, AldrichChemical Company) in toluene (15.0 mL) was added 3-amino-1,2-propanediolprotected as the FMOC carbamide (1.0 g, 3.2 mmol), followed by acatalytic amount of p-toluenesulfonic acid monohydrate (Aldrich ChemicalCompany). The reaction mixture was heated at reflux for 16 hrs with theremoval of water by azeotropic distillation in a Dean-Stark trap. Thereaction mixture was cooled to room temperature, partitioned intoluene/H₂O, washed 1×10% NaHCO₃, 3×H₂O, 1× brine, and dried (MgSO₄).The extract was concentrated under reduced pressure and crystallized(methanol/H₂O). The protected amine ketal was identified in thesupernatant, which was concentrated to afford 156 mg product. The freeamine was generated by treating the ketal with piperidine indichloromethane for 1 hr.

[0355] S) Di-(2-methyl-4-hydroxymethyl(glycineester)-1,3-dioxolane)-1,4-benzene (MC373). To a solution of FMOC-Glycine(690 mg, 2.3 mmol, NovaBiochem) in dichloromethane (4.0 mL) was addeddicyclohexylcarbodiimide (540 mg, 2.6 mmol, Aldrich Chemical Company).After 5 minutes, di-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene(240 mg, 770 μmol) was added followed by a catalytic amount of4-dimethylaminopyridine. After 20 min, the reaction mixture was filteredand concentrated (aspirator) to afford 670 mg of oil. The residue wastaken in tetrahydrofuran (4.0 mL) and piperidine (144 mg, 1.7 mmol) wasadded. The reaction was stirred at room temperature for 1 hr and addedto cold diethyl ether. The resulting solid was washed 3× diethyl etherto afford di-(2-methy-4-hydroxymethyl(glycineester)-1,3-dioxolane)-1,4,benzene. Molecular ion calculated forC₂₀H₂₈N₂O₈ 424, found m+1/z 425.2.

[0356] Synthesis of Polymers Containing Acid Labile Moieties:

[0357] T) Di-(2-methyl-4-hydroxymethyl(glyoxilic acidester)-1,3-dioxolane)-1,4-benzene: 1,4-Bis(3-aminopropyl)piperazineCopolymer (1:1) (MC228): To a solution ofdi-(2-methyl-4-hydroxymethyl(glyoxylic acid ester)-1,3-dioxolane)1,4-benzene (100 mg, 0.273 mmol) in dimethylformamide was added1,4-bis(3-aminopropyl)-piperazine (23 μL, 0.273 mmol, Aldrich ChemicalCompany) and the solution was heated to 80° C. After 16 hrs the solutionwas cooled to room temperature and precipitated with diethyl ether. Thesolution was decanted and the residue washed with diethyl ether (2×) anddried under vacuum to afford di-(2-methyl-4-hydroxymethyl(glyoxylic acidester)-1,3-dioxolane) 1,4-benzene: 1,4-bis(3-aminopropyl)-piperazinecopolymer (1:1).

[0358] By similar methods, the following polymers were constructed:

[0359] Di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene: 1,4-Bis(3-aminopropyl)piperazineCopolymer (1:1) (MC208).

[0360] Di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene: 1,4-Bis(3-aminopropyl)piperazineCopolymer (1:1) Reduced with NaCNBH₃ (MC301).

[0361] Di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene: 1,3-Diaminopropane Copolymer (1:1)(MC300).

[0362] Di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene: 3,3′-Diamino-N-methyldipropylamineCopolymer (1:1) (MC218).

[0363] Di-(2-methyl-4-hydroxymethyl(succinic semialdehydeester)-1,3-dioxolane)-1,4-benzene: Tetraethylenepentamine Copolymer(1:1) (MC217).

[0364] Di-(2-methyl-4-hydroxymethyl(glyoxilic acidester)-1,3-dioxolane)-1,4-benzene: 1,3-Diaminopropane Copolymer (1:1)(MC226).

[0365] Di-(2-methyl-4-hydroxymethyl(glyoxilic acidester)-1,3-dioxolane)-1,4-benzene: 3,3′-Diamino-N-methyldipropylamineCopolymer (1:1) (MC227).

[0366] U) Synthesis of 1,4-Bis(3-aminopropyl)piperazine—GlutaricDialdehyde Copolymer (MC140). 1,4-Bis(3-aminopropyl)piperazine (206 μL,0.998 mmol, Aldrich Chemical Company) was taken up in 5.0 mL H₂O.Glutaric dialdehyde (206 μL, 0.998 mmol, Aldrich Chemical Company) wasadded and the solution was stirred at room temperature. After 30 min, anadditional portion of H₂O was added (20 mL), and the mixture neutralizedwith 6 N HCl to pH 7, resulting in a red solution. Dialysis against H₂O(3×3L, 12,000-14,000 MWCO) and lyophilization afforded 38 mg (14%) ofthe copolymer.

[0367] By similar methods, the following polymers were constructed:

[0368] Diacetylbenzene-1,3-Diaminopropane Copolymer (1:1) (MC321)

[0369] Diacetylbenzene-Diamino-N-methyldipropylamine Copolymer (1:1)(MC322).

[0370] Diacetylbenzene-1,4-Bis(3-aminopropyl)piperazine Copolymer (1:1)(MC229)

[0371] Diacetylbenzene-Tetraethylenepentamine Copolymer (1:1) (MC323).

[0372] Glutaric Dialdehyde-1,3-Diaminopropane Copolymer (1:1) (MC324)

[0373] Glutaric Dialdehyde-Diamino-N-methyldipropylamine Copolymer (1:1)(MC325).

[0374] Glutaric Dialdehyde-Tetraethylenepentamine Copolymer (1:1)(MC326).

[0375] 1,4-Cyclohexanone-1,3-Diaminopropane Copolymer (1:1) (MC330)

[0376] 1,4-Cyclohexanone-Diamino-N-methyldipropylamine Copolymer (1:1)(MC33 1).

[0377] 1,4-Cyclohexanone-1,4-Bis(3-aminopropyl)piperazine Copolymer(1:1) (MC312)

[0378] 1,4-Cyclohexanone-Tetraethylenepentamine Copolymer (1:1) (MC332).

[0379] 2,4-Pentanone-1,4-Bis(3-aminopropyl)piperazine Copolymer (1:1)(MC340)

[0380] 2,4-Pentanone-Tetraethylenepentamine Copolymer (1:1) (MC347).

[0381] 1,5-Hexafluoro-2,4-Pentanone-1,4-Bis(3-aminopropyl)piperazineCopolymer (1:1) (MC339)

[0382] 1,5-Hexafluoro-2,4-Pentanone-Tetraethylenepentamine Copolymer(1:1) (MC346).

[0383] V) Synthesis of Poly-L-Glutamic acid (octamer)—GlutaricDialdehyde Copolymer (MC151): H₂N-SEQ ID NO: 11-NHCH₂CH₂NH₂ (; 5.5 mg,0.0057 mmol, Genosis) was taken up in 0.4 mL H₂O. Glutaric dialdehyde(0.52 μL, 0.0057 mmol, Aldrich Chemical Company) was added and themixture was stirred at room temperature. After 10 min the solution washeated to 70° C. After 15 hrs, the solution was cooled to roomtemperature and dialyzed against H₂O (2×2L, 3500 MWCO). Lyophilizationafforded 4.3 mg (73%) poly-glutamic acid (octamer)—glutaric dialdehydecopolymer.

[0384] W) Synthesis ofDi-(2-methyl-4-aminomethyl-1,3-dioxolane)-1,4-benzene—GlutaricDialdehyde Copolymer (MC352). To a solution ofdi-(2-methyl-4-aminomethyl-1,3-dioxolane)-1,4-benzene (23 mg, 75 μmol)in dimethylformamide (200 μL) was added glutaric dialdehyde (7.5 mg, 75μmol, Aldrich Chemical Company). The reaction mixture was heated at 80°C. for 6 hrs under nitrogen. The solution was cooled to room temperatureand used without further purification.

[0385] X) Synthesis of Di-(2-methy-4-hydroxymethyl(glycineester)-1,3-dioxolane)-1,4,benzene—Glutaric Dialdehyde Copolymer (MC357).To a solution of di-(2-methy-4-hydroxymethyl(glycineester)-1,3-dioxolane)-1,4,benzene (35 mg, 82 μmol) in dimethylformamide(250 μL) was added glutaric dialdehyde (8.2 mg, 82 μmol, AldrichChemical Company). The reaction mixture was heated at 80° C. for 12 hrs.The solution was cooled to room temperature and used without furtherpurification.

[0386] Y) Synthesis of Polyvinyl(2-phenyl-4-hydroxymethyl-1,3-dioxolane)from the reaction of Polyvinylphenyl Ketone and Glycerol: Polyvinylphenyl ketone (500 mg, 3.78 mmol, Aldrich Chemical Company) was taken upin 20 mL dichloromethane. Glycerol (304 μL, 4.16 mmol, Acros ChemicalCompany) was added followed by p-toluenesulfonic acid monohydrate (108mg, 0.57 mmol, Aldrich Chemical Company). Dioxane (10 mL) was added andthe solution was stirred at room temperature overnight. After 16 hrs,TLC indicated the presence of ketone. The solution was concentratedunder reduced pressure, and the residue dissolved in dimethylformamide(7 mL). The solution was heated to 60° C. for 16 hrs. After 16 hrs, TLCindicated the ketone had been consumed. Dialysis against H₂O (1×3L, 3500MWCO), followed by lyophilization resulted in 606 mg (78%) of the ketal.Ketone was not observed in the sample by TLC analysis, however, upontreatment with acid, the ketone was again detected.

[0387] Z) Synthesis of Polyvinyl(2-methyl-4-hydroxymethyl(succinicanhydride ester)-1,3-dioxolane: To a solution ofpolyvinyl(2-methyl-4-hydroxymethyl-1,3-dioxolane) (220 mg, 1.07 mmol) indichloromethane (5 mL) was added succinic anhydride (161 mg, 1.6 mmol,Sigma Chemical Company), followed by diisopropylethyl amine (0.37 mL,2.1 mmol, Aldrich Chemical Company) and the solution was heated atreflux. After 16 hrs, the solution was concentrated, dialyzed againstH₂O (1×3L, 3500 MWCO), and lyophilized to afford 250 mg (75%) of theketal acid polyvinyl(2-methyl-4-hydroxymethyl(succinic anhydrideester)-1,3-dioxolane.

[0388] AA) Synthesis of Ketal from Polyvinyl Alcohol and 4-AcetylbutyricAcid: Polyvinylalcohol (200 mg, 4.54 mmol, 30,000-60,000 MW, AldrichChemical Company) was taken up in dioxane (10 mL). 4-acetylbutyric acid(271 μL, 2.27 mmol, Aldrich Chemical Company) was added followed byp-toluenesulfonic acid monohydrate (86 mg, 0.45 mmol, Aldrich ChemicalCompany). After 16 hrs, TLC indicated the presence of ketone. Thesolution was concentrated under reduced pressure, and the residuedissolved in dimethylformamide (7 mL). The solution was heated to 60° C.for 16 hrs. After 16 hrs, TLC indicated the loss of ketone in thereaction mixture. Dialysis against H₂O (1×4L, 3500 MWCO), followed bylyophilization resulted in 145 mg (32%) of the ketal. Ketone was notobserved in the sample by TLC analysis, however, upon treatment withacid, the ketone was again detected.

[0389] AB) Partial Esterification of Poly-Glutamic Acid withDi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (MC 196). To asolution of poly-L-glutamic acid (103 mg, 792 μmol, 32,000 MW, SigmaChemical Company) in sodium phosphate buffer (30 mM) was added1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (129 mg, 673μmol, Aldrich Chemical Company), followed bydi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (25.0 mg, 80.5μmol), and a catalytic amount of 4-dimethylaminopyridine. After 12 hrs,the reaction mixture was dialyzed against water (2×1L, 12,000-14,000MWCO) and lyophilized to afford 32 mg of poly-glutamic acid partiallyesterified with di-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene.

[0390] AC) Aldehyde Derivatization of the Poly-Glutamic Acid PartiallyEsterified with Di-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene:To a solution of succinic semialdehyde (2.4 mg, 23 μmol, AldrichChemical Company) in water (100 μL) was added1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (4.7 mg, 2.4μmol, Aldrich Chemical Company) followed by N-hydroxysuccinimide (2.8mg, 24 μmol, Aldrich Chemical Company). The reaction was stirred at roomtemperature for 20 min. Formation of the N-hydroxysuccinic ester ofsuccinic semialdehyde was confirmed by mass spectrometry.

[0391] Poly-glutamic acid partially esterified withdi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (15.0 mg, 115μmol) was taken up in water (100 μL) and added to the N-hydroxysuccinicester of succinic semialdehyde, followed by a crystal of4-dimethylaminopyridine. The reaction mixture was stirred overnight atroom temperature. After 12 hrs the reaction mixture was dialyzed againstwater (2×1L, 12,000-14,000 MWCO) and lyophilized to afford 3.0 mg. Afterdialysis the product tested positive for aldehyde content with2,4-di-nitrophenylhydrazine.

[0392] AD) Synthesis of a Silyl Ether from Polyvinylalcohol and3-Aminopropyl-trimethoxysilane (MC221): To a solution ofpolyvinylalcohol (520 mg, 11.8 mmol (OH), 30,000-70,000 MW, SigmaChemical Company) in dimethylformamide (4 mL) was added3-aminopropyltrimethoxysilane (1.03 mL, 5.9 mmol, Aldrich ChemicalCompany) and the solution was stirred at room temperature. After 2.5hrs, a 20 μL aliquot of the reaction mixture was removed and added topDNA (pCI Luc) (100 μg) in 25 mM HEPES buffer at pH 7.5 (500 μL) to testfor polyamine formation (pDNA:amine 1:3). Particle sizing (BrookhavenInstruments Coporation, ZetaPlus Particle Sizer, I90, 532 nm) indicatedan effective diameter of 3000 nm (1.3 mcps) indicating pDNA condensationand particle formation. An aliquot of 1 N HCl (40 μL) was added to thesample, and the particle size was again measured. After 1 min ofexposure to the acidic conditions, the particle size was 67,000 nm (600kcps). After 10 min, particles were no longer present within the sample.The sample was dried under high vacuum to afford 1.0 g (83%) whitesolid.

[0393] By similar methods, the following polymers were constructed:

[0394] Silyl Ether from Poly-L-Arginine/-L-Serine(3:1) and3-Aminopropyltrimethoxysilane (2:1) (MC358):Poly-L-Arginine/-L-Serine(3:1) (20,000-50,000 MW, Sigma ChemicalCompany), 3-Aminopropyltrimethoxysilane (Aldrich Chemical Company)

[0395] Silyl Ether from Poly-DL-Serine and 3-Aminopropyltrimethoxysilane(3:1) (MC366). Poly-DL-Serine (5,000-15,000 MW, Sigma Chemical Company),3-Aminopropyl-trimethoxysilane (Aldrich Chemical Company)

[0396] Silyl Ether from Poly-DL-Serine and 3-Aminopropyltrimethoxysilane(2:1) (MC367).

[0397] Poly-DL-Serine (5,000-15,000 MW, Sigma Chemical Company),3-Aminopropyl-trimethoxysilane (Aldrich Chemical Company)

[0398] Silyl Ether from Poly-DL-Serine andN-[3-(Triethoxysilyl)propyl]-4,5-dihydroimidizole (3:1) (MC369).Poly-DL-Serine (5,000-15,000 MW, Sigma Chemical Company)

[0399] N-[3-(Triethoxysilyl)propyl]-4,5-dihydroimidizole (UnitedChemical Technologies, Incorporated)

[0400] Silyl Ether from Poly-DL-Serine andN-Trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (3:1) (MC370).Poly-DL-Serine (5,000-15,000 MW, Sigma Chemical Company)

[0401] N-Trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (UnitedChemical Technologies, Incorporated)

[0402] Silazane from Poly-L-Lysine and 3-Aminopropyltrimethoxysilane(2:1) (MC360).

[0403] Poly(1,1-Dimethylsilazane) Tolemer (MC222): Sample was obtainedfrom United Chemical Technologies, Incorporated.

Example 2

[0404] Transfection with pH-Sensitive Compounds and/or Membrane ActiveAgents

[0405] A) In Vitro Transfection with DNA-PLL-KL₃ and dimethylmaleamicKL₃: To a complex of plasmid DNA pCIluc (10 μg/mL, 0.075 mM inphosphate, 2.6 μg/μL pCIluc; prepared according to Danko, I., Williams,P., Herweijer, H. Zhang, G., Latendresse, J. S., Bock, I., Wolff, J. A.Hum. Mol. Genetics 1997, 6, 1435.) and poly-L-lysine (40 μg/mL) in 0.5mL of 5 mM HEPES pH 7.5 was added succinylated poly-L-lysine (34,000 MW,Aldrich Chemical), 2,3-dimethylmaleamic melittin and2,3-dimethylmaleamic KL₃. The DNA-poly-L-lysine-2,3-dimethylmaleamicpeptide complexes were then added (200 μL) to wells containing 3T3 mouseembryonic fibroblast cells in 290 mM glucose and 5 mM HEPES buffer pH7.5. After 1.5 h, the glucose media was replaced with Dubelco's modifiedEagle Media and the cells were allowed to incubate for 48 h. The cellswere then harvested and then assayed for luciferase expression aspreviously reported (Wolff, J. A., Malone, R. W., Williams, P., Chong,W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transfer intomouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507 (EG&GBerthold, Bad-Wildbad, Germany) luminometer was used. The amount oftransfection was reported in relative light units and is the averagetransfection for two separate wells of cells. Relative Light Units(Relative to Peptide Succinylated poly-L-lysine) Succinylatedpoly-L-lysine 6410 (1) KL₃ 261 (0.04) 2,3-dimethylmaleamic KL₃ 49535(7.7)

[0406] B) In Vitro Transfection with DNA-PLL complexes withdimethylmaleamic KL₃ and dimethylmaleamic KL₃-PLL: To a complex ofplasmid DNA pCIluc (10 μg/mL, prepared according to Danko, I., Williams,P., Herweijer, H. Zhang, G., Latendresse, J. S., Bock, I., Wolff, J. A.Hum. Mol. Genetics 1997, 6, 1435.) and poly-L-lysine (40 μg/mL) in 0.5mL water was added 10 mg of 2,3-dimethylmaleamic —KL₃-PLL or2,3-dimethylmaleamic —KL₃. The DNA-poly-L-lysine-2,3-dimethylmaleamicpeptide complexes were then added (200 μL) to a well containing 3T3mouse embryonic fibroblast cells in opti-MEM. After 4 h, the media wasreplaced with 90% Dubelco's modified Eagle Media and 10% fetal bovineserum the cells were then allowed to incubate for 48 h. The cells werethen harvested and then assayed for luciferase expression as previouslyreported (Wolff, J. A., Malone, R. W., Williams, P., Chong, W., Acsadi,G., Jani, A. and Felgner, P. L. Direct gene transfer into mouse musclein vivo. Science, 1465-1468, 1990.). A Lumat LB 9507 (EG&G Berthold,Bad-Wildbad, Germany) luminometer was used. The amount of transfectionwas reported in relative light units and is the average transfection fortwo separate wells of cells. 2,3-dimethylmaleamic peptide Relative LightUnits 2,3-dimethylmaleamic KL₃  20927 2,3-dimethylmaleamic KL₃-PLL130478

[0407] C) In Vitro Transfection with DNA-PLL complexes withdimethylmaleamic KL₃-PLL, 2-propionic-3-methylmaleamic KL₃-PLL, andsuccinimic KL₃-PLL: To a complex of plasmid DNA pCIluc (10 μg/mL,prepared according to Danko, I., Williams, P., Herweijer, H. Zhang, G.,Latendresse, J. S., Bock, I., Wolff, J. A. Hum. Mol. Genetics 1997, 6,1435.) and poly-L-lysine (40 μg/mL) in 0.5 mL water was added 25 μg of2,3-dimethylmaleamic —KL₃-PLL, 2-propionic-3-methylmaleamic KL₃-PLL, andsuccinimic KL₃-PLL. The DNA-poly-L-lysine-peptide complexes were thenadded (200 μL) to a well containing 3T3 mouse embryonic fibroblast cellsin opti-MEM media. After 4 h, the media was replaced with 90% Dubelco'smodified Eagle Media and 10% fetal bovine serum the cells were thenallowed to incubate for 48 h. The cells were then harvested and thenassayed for luciferase expression as previously reported (Wolff, J. A.,Malone, R. W., Williams, P., Chong, W., Acsadi, G., Jani, A. andFelgner, P. L. Direct gene transfer into mouse muscle in vivo. Science,1465-1468, 1990.). A Lumat LB 9507 (EG&G Berthold, Bad-Wildbad, Germany)luminometer was used. The amount of transfection was reported inrelative light units and is the average transfection for two separatewells of cells. Modified peptide Relative Light Units2,3-dimethylmaleamic KL₃-PLL  96221 2-propionic-3-methylmaleamic KL₃-PLL102002 succinimic KL₃-PLL  21206

[0408] D) In Vitro Transfection with DNA-PLL with2,3-dimethylmaleamic-modified lipids: To a complex of plasmid DNA pCIluc(10 μg/mL, 2.2 μg/μL pCIluc; prepared according to Danko, I., Williams,P., Herweijer, H. Zhang, G., Latendresse, J. S., Bock, I., Wolff, J. A.Hum. Mol. Genetics 1997, 6, 1435.) and poly-L-lysine (40 μg/mL) in 0.5mL of deionized water was added 800 μg glycine followed by 40 μg2,3-dimethylmaleic DOG,2,3-dimethylmaleamicMC213,2,3-dimethylmaleamicMC303, or2,3-dimethylmaleamic-DOPE. TheDNA-poly-L-lysine-2,3-dimethylmaleamic-modified lipids were then added(200 μL) to a well containing opti-MEM media. After 4 h, the media wasreplaced with 90% Dubelco's modified Eagle Media and 10% fetal bovineserum the cells were then allowed to incubate for 48 h. The cells werethen harvested and then assayed for luciferase expression as previouslyreported (Wolff, J. A., Malone, R. W., Williams, P., Chong, W., Acsadi,G., Jani, A. and Felgner, P. L. Direct gene transfer into mouse musclein vivo. Science, 1465-1468, 1990.). A Lumat LB 9507 (EG&G Berthold,Bad-Wildbad, Germany) luminometer was used. The amount of transfectionwas reported in relative light units and is the average transfection fortwo separate wells of cells. Relative Light Units2,3-dimethylmaleamic-modified lipids (Relative topoly-L-lysine) No lipid6000 (1) MC213 91356 (15) MC303 469756 (78) DOPE 243359 (40) DOG 193624(32)

[0409] E) Transfection of HELA Cells with Histone HI and the MembraneActive peptide melittin, dimethylmaleic modified melittin or succinicanhydride modifed melittin: Three complexes were formed:

[0410] Complex I) To 300 μL Opti-MEM was added Histone H1(12 μg, SigmaCorporation) followed by the peptide Melittin (20 μg) followed by pDNA(pCI Luc, 4 μg).

[0411] Complex II) To 300 μL Opti-MEM was added Histone H1(12 μg, SigmaCorporation) followed by the 2,3-dimethylmaleic modified peptideMelittin (20 μg) followed by pDNA (pCI Luc, 4 μg).

[0412] Complex III) To 300 μL Opti-MEM was added Histone H1(12 μg, SigmaCorporation) followed by the succinic anhydride modified peptideMelittin (20 μg) followed by pDNA (pCI Luc, 4 μg).

[0413] Transfections were carried out in 35 mm wells. At the time oftransfection, HELA cells, at approximately 60% confluency, stored incomplete growth media, DMEM with 10% fetal bovine serum (Sigma). 150 μLof complex was added to each After an incubation of 48 hours, the cellswere harvested and the lysate was assayed for luciferase expression aspreviously reported (Wolff, J. A., Malone, R. W., Williams, P., Chong,W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transfer intomouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507 (EG&GBerthold, Bad-Wildbad, Germany) luminometer was used. The amount oftransfection was reported in relative light units and is the averagetransfection for two separate wells of cells.

[0414] Results:

[0415] Complex I: RLU=2,161

[0416] Complex II: RLU=105,909

[0417] Complex III: RLU=1,056

[0418] The 2,3-dimethylmaleic modification of the peptide melittinallows the peptide to complex with the cationic protein Histone HI andthen cleave to release and reactivate in the lowered pH encountered bythe complex in the cellular endosomal compartment. This caused asignificant increase in luciferase expression over either unmodifiedmelittin peptide or melittin peptide modified with succinic anhydridewhich allows complexing with Histone H1 but will not cleave in loweredpH.

[0419] F) Transfection of 3T3 Cells with Dioleoyl1,2-Diacyl-3-Trimethylammonium-Propane (DOTAP) and the membrane activepeptide KL3 conjugated to dimethylmaleic modified Polyallylamine(DM-PAA-KL3) and poly-L-lysine orL-cystine-1,4-bis(3-aminopropyl)piperazine copolymer.

[0420] Three complexes were formed:

[0421] Complex I) To 250 μL 25 mM HEPES pH8.0 was added DOTAP 300 μg,Avanti Polar Lipids Inc)

[0422] Complex II) To 250 μL 25 mM HEPES pH8.0 was added DOTAP(300 μg,Avanti Polar Lipids Inc) followed by DM-PAA-KL₃ (10 μg) followed bypoly-L-lysine (10 μg, Sigma).

[0423] Complex II) To 250 μL 25 mM HEPES pH8.0 was added DOTAP(300 μg,Avanti Polar Lipids Inc) followed by DM-PAA-KL₃ (10 μg) followed byL-cystine-1,4-bis(3-aminopropyl)piperazine copolymer (10 μg).

[0424] Liposomes for each complex were formed by 5 minutes of bathsonication then purified in batch by addition of 250 ul of DEAE sephadexA-25. DNA (25 ug, pCILuc)was then added to the supernatant containingthe purified liposomes of each complex.

[0425] Transfections were carried out in 35 mm wells. At the time oftransfection, 3T3 cells,at approximately 60% confluency, stored incomplete growth media, DMEM with 10% fetal bovine serum (Sigma). 50 μLof complex was added to each well. After an incubation of 48 hours, thecells were harvested and the lysate was assayed for luciferaseexpression as previously reported (Wolff, J. A., Malone, R. W.,Williams, P., Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Directgene transfer into mouse muscle in vivo. Science, 1465-1468, 1990.). ALumat LB 9507 (EG&G Berthold, Bad-Wildbad, Germany) luminometer wasused. The amount of transfection was reported in relative light unitsand is the average transfection for two separate wells of cells.

[0426] Results:

[0427] Complex I: RLU=167

[0428] Complex IT: RLU=60,092

[0429] Complex III: RLU =243,986

[0430] The 2,3-dimethylmaleic modification of DM-PAA-KL3 allows thepolymer to complex with the cationic polymerL-cystine-1,4-bis(3-aminopropyl)piperazine copolymer and then cleavageof the 2,3-dimethylmaleamic group to release and reactivate in thedisulfide reducing environment encountered by the complex in the cell.This caused a significant increase in luciferase expression over eitherDOTAP complexes alone or DM-PAA-KL3 complexed with poly-L-lysine thatwill not cleave in the reducing environment encountered by the complexin the cell.

[0431] G) Transfection of3T3 Cells with Complexes of pCI LucpDNA/Cationic Polymers Caged with Compounds Containing Acid LabileMoieties.

[0432] Several complexes were formed:

[0433] Complex I: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400 μL)was added LT-1® (60 μg, Mirus Corporation).

[0434] Complex II: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added PLL (36 μg in 3.6 μL H₂O, 32,000 MW, Sigma ChemicalCompany).

[0435] Complex III: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added PLL (36 μg in 3.6 μL H₂O, 32,000 MW, Sigma ChemicalCompany) followed by DTBP (60 μg in 6 μL H₂O, Pierce Chemical Company).

[0436] Complex IV: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added PLL (36 μg in 3.6 μL H₂O, 32,000 MW, Sigma ChemicalCompany) followed by DTBP (60 μg in 6 μL H₂O, Pierce Chemical Company)followed by N,N′-dioleoyl-1,4-bis(3-aminopropyl)piperazine (10 μg, 2μg/μL in EtOH).

[0437] Complex V: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400 μL)was added PLL (36 μg in 3.6 μL H₂O, 32,000 MW, Sigma Chemical Company)followed by MC211 (87 μg in 8.7 μL dimethylformamide).

[0438] Complex VI: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added PLL (36 μg in 3.6 μL H₂O, 32,000 MW, Sigma ChemicalCompany) followed by MC211 (87 μg in 8.7 μL dimethylformamide) followedby N,N′-dioleoyl-1,4-bis(3-aminopropyl)piperazine (10 μg, 2 μg/μL inEtOH).

[0439] Complex VII: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added Histone H1 (120 μg in 12 μL H₂O, Sigma Chemical Company).

[0440] Complex VIII: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added Histone H1 (120 μg in 12 μL H₂O, Sigma Chemical Company)followed by DTBP (100 μg in 10 μL H₂O, Pierce Chemical Company).

[0441] Complex IX: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added Histone H1 (120 μg in 12 μL H₂O, Sigma Chemical Company)followed by DTBP (100 μg in 10 μL H₂O, Pierce Chemical Company) followedby N,N′-dioleoyl-1,4-bis(3-aminopropyl)piperazine (10 μg, 2 μg/μL inEtOH).

[0442] Complex X: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400 μL)was added Histone H1 (120 μg in 12 μL H₂O, Sigma Chemical Company)followed by MC211 (145 μg in 14.5 μL dimethylformamide).

[0443] Complex XI: To a solution of pDNA (pCI Luc, 20 μg) in H₂O (400μL) was added Histone H1 (120 μg in 12 μL H₂O, Sigma Chemical Company)followed by MC211 (145 μg in 14.5 μL dimethylformamide) followed byN,N′-dioleoyl-1,4-bis(3-aminopropyl)piperazine (10 μg, 2 μg/μL in EtOH).

[0444] Transfections were carried out in 35 mm wells. At the time oftransfection, 3T3 cells, at approximately 50% confluency, were washedonce with PBS (phosphate buffered saline), and subsequently stored inserum-free media (2.0 mL, Opti-MEM, Gibco-BRL). 100 μL of complex wasadded to each well. After a 3.25 h incubation period at 37° C., themedia containing the complexes was aspirated from the cells, andreplaced with complete growth media, DMEM with 10% fetal bovine serum(Sigma). After an additional incubation of 48 hours, the cells wereharvested and the lysate was assayed for luciferase expression aspreviously reported (Wolff, J. A., Malone, R. W., Williams, P., Chong,W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transfer intomouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507 (EG&GBerthold, Bad-Wildbad, Germany) luminometer was used. The amount oftransfection was reported in relative light units and is the averagetransfection for two separate wells of cells. Results: Complex I:2,467,529 RLU Complex II: 10,748 RLU Complex III: 377 RLU Complex IV:273 RLU Complex V: 7,174 RLU Complex VI: 71,338 RLU Complex VII: 162,166RLU Complex VIII: 1,336 RLU Complex IX: 162,166 RLU Complex X: 51,003RLU Complex XI: 3,949,177 RLU

[0445] The transfection results indicate that caging cationic pDNAcomplexes (PLL or Histone H1) with DTBP reduce the amount of expressedluciferine. Caging of the cationic pDNA complexes with MC211 results inan increased amount of expressed luciferine relative to the DTBPexamples.

[0446] In Vivo Transfections

[0447] H) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Polymer Containing Acid Labile Moieties.

[0448] H1) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/1,4-Bis(3-aminopropyl)piperazine Glutaric Dialdehyde Copolymer (MC140).

[0449] Three complexes were prepared as follows:

[0450] Complex I: pDNA (pCI Luc, 50 μg) in 12.5 mL Ringers.

[0451] Complex II: pDNA (pCI Luc, 50 μg) was mixed with1,4-bis(3-aminopropyl)piperazine glutaric dialdehyde copolymer (50 μg)in 1.25 mL HEPES 25 mM, pH 8. This solution was then added to 11.25 mLRingers.

[0452] Complex III: pDNA (pCI Luc, 50 μg) was mixed with poly-L-lysine(94.5 μg, MW 42,000, Sigma Chemical Company) in 12.5 mL Ringers.

[0453] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. Results: 2.5mL injections Complex I: 3,692,000 RLU Complex II: 1,047,000 RLU ComplexIII: 4,379 RLU

[0454] Results indicate an increased level of pCI Luc DNA expression inpDNA/1,4-bis(3-aminopropyl)piperazine glutaric dialdehyde copolymercomplexes over pCI Luc DNA/poly-L-lysine complexes. These results alsoindicate that the pDNA is being released from thepDNA/1,4-Bis(3-aminopropyl)piperazine-glutaric dialdehyde copolymercomplexes, and is accessible for transcription.

[0455] H2A) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Imine Containing Copolymer's: By similar methods described above,several additional complexes were prepaired from imine containingpolymers at a 3:1 charge ratio of polycation to pDNA. Complex I: pDNA(pCI Luc, 50 μg) Complex II: pDNA (pCI Luc, 50 μg)/MC229

[0456] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. The amountof transfection was reported in relative light units and is the averagetransfection for n separate animals. Results: 2.5 mL injections ComplexI: n = 3 3,430,000 RLU Complex II: n = 3 21,400,000 RLU

[0457] The results indicate that the pDNA is being released from thepDNA/imine containing copolymer complexes, and is accessible fortranscription.

[0458] H2B) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Imine Containing Copolymer's. By similar methods described above,several additional complexes were prepaired from imine containingpolymers at a 3:1 charge ratio of polycation to pDNA. Complex I: pDNA(pCI Luc, 50 μg) Complex II: pDNA (pCI Luc, 50 μg)/MC140-2 Complex III:pDNA (pCI Luc, 50 μg)/MC312

[0459] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. The amountof transfection was reported in relative light units and is the averagetransfection for n separate animals. Results: 2.5 mL injections ComplexI: n = 1 9,460,000 RLU Complex II: n = 3 7,730,000 RLU Complex III: n =3 16,300,000 RLU

[0460] The results indicate that the pDNA is being released from thepDNA/imine containing copolymer complexes, and is accessible fortranscription.

[0461] H3A) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Ketal Containing Copolymers. By similar methods described above,several complexes were prepared at a 3:1 charge ratio of polycation topDNA: Complex I: pDNA (pCI Luc, 50 μg) Complex II: pDNA (pCI Luc, 50μg)/PLL-DTBP(Pierce Chemical Co., 50%) Complex III: pDNA (pCI Luc, 50μg)/PLL-MC211(50%) Complex IV: pDNA (pCI Luc, 50 μg)/MC228 Complex V:pDNA (pCI Luc, 50 μg)/MC208

[0462] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. The amountof transfection was reported in relative light units and is the averagetransfection for n separate animals. Results: 2.5 mL injections ComplexI: n = 3 2,440,000 RLU Complex II: n = 3 110,000 RLU Complex III: n = 3292,000 RLU Complex IV: n = 3 119,000 RLU Complex V: n = 3 3,590,000 RLU

[0463] H3B) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Ketal Containing Copolymers. By similar methods described above,several complexes were prepared at a 3:1 charge ratio of polycation topDNA: Complex I: pDNA (pCI Luc, 50 μg) Complex II: pDNA (pCI Luc, 50μg)/PLL-MC225(50%) Complex III: pDNA (pCI Luc, 50 μg)/MC217 Complex IV:pDNA (pCI Luc, 50 μg)/MC218

[0464] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. The amountof transfection was reported in relative light units and is the averagetransfection for n separate animals. Results: 2.5 mL injections ComplexI: n = 3 5,940,000 RLU Complex II: n = 3 611,000 RLU Complex III: n = 35,220,000 RLU Complex IV: n = 3 7,570,000 RLU

[0465] H3C) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Ketal Containing Copolymers. By similar methods described above,several complexes were prepared at a 3:1 charge ratio of polycation topDNA: Complex I: pDNA (pCI Luc, 50 μg) Complex II: pDNA (pCI Luc, 50μg)/MC208 Complex III: pDNA (pCI Luc, 50 μg)/MC301

[0466] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. The amountof transfection was reported in relative light units and is the averagetransfection for n separate animals. Results: 2.5 mL injections ComplexI: n = 3 3,430,000 RLU Complex II: n = 2 9,110,000 RLU Complex III: n =3 8,570,000 RLU

[0467] Results indicate an increased level of pCI Luc DNA expression inComplex III and Complex VII relative to Complex II indicating that whenthe acid labile homobifunctional amine reactive system (MC211, MC225) isused, more pDNA is accessible for transcription relative to thenon-labile homobifunctional amine reactive system (DTBP). These resultsalso indicate that the pDNA is being released from the pDNA/ketalcontaining copolymer complexes, and is accessible for transcription.

[0468] H4) Mouse Tail Vein Injections of Complexes of pDNA (pCILuc)/Silicon Containing Polymers. By similar methods described above,several complexes were prepared at a 3:1 charge ratio of polycation topDNA: Complex I: pDNA (pCI Luc, 50 μg) Complex II: pDNA (pCI Luc, 50μg)/MC221 Complex III: pDNA (pCI Luc, 50 μg)/MC222 Complex IV: pDNA (pCILuc, 50 μg)/MC223 Complex V: pDNA (pCI Luc, 50 μg)/MC358 Complex VI:pDNA (pCI Luc, 50 μg)/MC358 recharged with SPLL (MC359) Complex VII:pDNA (pCI Luc, 50 μg)/MC360 Complex VIII: pDNA (pCI Luc, 50μg)/Poly-L-Arginine/-L-Serine(3:1) Complex IX: pDNA (pCI Luc, 50μg)/MC366 Complex X: pDNA (pCI Luc, 50 μg)/MC367 Complex XI: pDNA (pCILuc, 50 μg)/MC369 Complex XII: pDNA (pCI Luc, 50 μg)/MC370

[0469] 2.5 mL tail vein injections of 2.5 mL of the complex werepreformed as previously described. Luciferase expression was determinedas previously reported (Wolff, J. A., Malone, R. W., Williams, P.,Chong, W., Acsadi, G., Jani, A. and Felgner, P. L. Direct gene transferinto mouse muscle in vivo. Science, 1465-1468, 1990.). A Lumat LB 9507(EG&G Berthold, Bad-Wildbad, Germany) luminometer was used. The amountof transfection was reported in relative light units and is the averagetransfection for n separate animals. Results: 2.5 mL injections ComplexI:  n = 14 14,564,000 RLU Complex II:  n = 14 14,264,000 RLU ComplexIII: n = 9 13,449,000 RLU Complex IV: n = 3 6,927,000 RLU Complex V: n =3 10,049,000 RLU Complex VI: n = 3 13,879,000 RLU Complex VII: n = 310,599,000 RLU Complex VIII: n = 3 638,000 RLU Complex IX: n = 312,597,000 RLU Complex X: n = 3 13,093,000 RLU Complex XI: n = 325,129,000 RLU Complex XII: n = 3 15,857,000 RLU

[0470] The results indicate that the pDNA is being released from thepDNA/Silicon containing polycation complexes, and is accessible fortranscription. Additionally, the results indicate that complex VIII(does not contain the silicon) is much less effective in the assay thanis complex V. Additionally, the results indicate that upon the additionof a third layer, a polyanion (complex VI), the complex containing thesilicon polymer allows for pDNA transcription.

[0471] G) Mouse Intramuscular Injections of Complexes of pDNA (pCILuc)/Polymer Containing Acid Labile Moiety(s). Complexes were preparedas follows: Complex I: pDNA. pDNA (pCI Luc, 60 μg, 27 μl) was added to0.9% saline (1173 μL). Complex II: pDNA/MC208 (1:0.5). To a solution ofpDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline (1173 μL) was added MC208(0.19 μL, in dimethylformamide). Complex III: pDNA/MC208 (1:3). To asolution of pDNA (pCI Luc, 60 μg) in 0.9% saline (1161 μL) was addedMC208 (12 μL, in dimethylformamide). Complex IV: pDNA/MC301 (1:0.5). Toa solution of pDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline (1173 μL) wasadded MC301 (0.15 μL, in dimethylformamide). Complex V: pDNA/MC301(1:3). To a solution of pDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline(1172 μL) was added MC301 (0.88 μL, in dimethylformamide). Complex VI:pDNA/MC229 (1:0.5). To a solution of pDNA (pCI Luc, 60 μg, 27 μL) in0.9% saline (1173 μL) was added MC229 (0.09 μL, in dimethylformamide).Complex VII: pDNA/MC229 (1:3). To a solution of pDNA (pCI Luc, 60 μg, 27μL) in 0.9% saline (1172 μL) was added MC229 (0.59 μL, indimethylformamide). Complex VIII: pDNA/MC140 (1:0.5). To a solution ofpDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline (1173 μL) was added MC140(0.08 μL, in dimethylformamide). Complex IX: pDNA/MC140 (1:3). To asolution of pDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline (1173 μL) wasadded MC140 (0.48 μL, in dimethylformamide). Complex X: pDNA/MC312(1:0.5). To a solution of pDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline(1173 μL) was added MC312 (0.08 μL, in dimethylformamide). Complex XI:pDNA/MC312 (1:3). To a solution of pDNA (pCI Luc, 60 μg, 27 μL) in 0.9%saline (1173 μL) was added MC312 (0.50 μL, in dimethylformamide).Complex XII: pDNA/MC217 (1:0.5). To a solution of pDNA (pCI Luc, 60 μg,27 μL) in 0.9% saline (1173 μL) was added MC217 (0.11 μL, indimethylformamide). Complex XIII: pDNA/MC217 (1:3). To a solution ofpDNA (pCI Luc, 60 μg, 27 μL) in 0.9% saline (1172 μL) was added MC217(0.69 μL, in dimethylformamide). Complex XIV: pDNA/MC221 (1:3). To asolution of pDNA (pCI Luc, 40 μg, 18 μL) in 0.9% saline (781 μL) wasadded MC221 (1.1 μL, in H₂O). Complex XV: pDNA/MC222 (1:3). To asolution of pDNA (pCI Luc, 40 μg, 18 μL) in 0.9% saline (782 μL) wasadded MC222 (0.40 μL, in H₂O). Complex XVI: pDNA. pDNA (pCI Luc, 100 μg,45 μL) was added to 0.9% saline (1955 μL). Complex XVII: pDNA/PLL (1:3).To a solution of pDNA (pCI Luc, 100 μg, 45 μL) in 0.9% saline (1943 μL)was added PLL (32,000 MW, Sigma Chemical Company, 12 μL, in H₂O).Complex XVIII: pDNA/PEI (1:3). To a solution of pDNA (pCI Luc, 100 μg,45 μL) in 0.9% saline (1,945 μL) was added PEI (25,000 MW, SigmaChemical Company, 10 μL (10 mg/mL), in H₂O). Complex XIX: pDNA/HistoneH1(1:3). To a solution of pDNA (pCI Luc, 100 μg, 45 μL) in 0.9% saline(1.889 μL) was added Histone H1 (Sigma Chemical Company, 66 μL (10mg/mL), in H₂O).

[0472] Direct muscle injections of 200 μL of the complex were preformedas previously described (See Budker, V., Zhang, G., Danko, I., Williams,P., and Wolff, J., “The Efficient Expression Of IntravascularlyDelivered DNA In Rat Muscle,” Gene Therapy 5, 272-6(1998); Wolff, J. A.,Malone, R. W., Williams, P., Chong, W., Acsadi, G., Jani, A. andFelgner, P. L. Direct gene transfer into mouse muscle in vivo. Science,1465-1468, 1990. Seven days post injection, the animals were sacrificed,and the muscle harvested. Samples were homogenized in lux buffer (1 mL),and centrifuged for 15 minutes at 4000 RPM. Luciferase expression wasdetermined as previously reported. Results reported are for the averageexpression for the quadracep muscle (left and right quadracep muscle/2)per number of animals (n). Results: Complex I: n = 3 473,148 RLU ComplexII: n = 3 328,054 RLU Complex III: n = 3 104,348 RLU Complex IV: n = 3228,582 RLU Complex V: n = 3 259,007 RLU Complex VI: n = 3 989,905 RLUComplex VII: n = 3 286,118 RLU Complex VIII: n = 3 433,177 RLU ComplexIX: n = 3 46,727 RLU Complex X: n = 3 365,440 RLU Complex XI: n = 3 454RLU Complex XII: n = 3 1,386,208 RLU Complex XIII: n = 3 295 RLU ComplexXIV: n = 2 352,639 RLU Complex XV: n = 2 459,695 RLU Complex XVI:  n =10 1,281,401 RLU Complex XVII:  n = 10 2,789 RLU Complex XVIII:  n = 10340 RLU Complex XIX:  n = 10 357 RLU

[0473] The complexes prepared from pCI Luc DNA and polymers containingacid labile moities are effective in direct muscle injections. Theluciferase expression indicates that the pDNA is being released from thecomplex and is accessible for transcription.

Example 3

[0474] Synthesis of Peptides and Polyions

[0475] A) Peptide synthesis. Peptide syntheses were performed usingstandard solid phase peptide techniques using FMOC chemistry. N-terminalacryloyl 6-aminohexanoyl-SEQ ID NO: 10-CO₂ (AcKL₃) was synthesizedaccording to published procedure (O'Brien-Simpson, N. M., Ede, N. J.,Brown, L. E., Swan, J., Jackson, D. C J. Am. Chem. Soc. 1997, 119,1183).

[0476] B) Coupling KL₃ to poly(allylamine). To a solution ofpoly(allylamine) (2 mg) in water (0.2 mL) was added KL3 (0.2 mg, 2.5 eq)and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (1 mg,150 eq). The reaction was allowed to react for 16 h and then the mixturewas placed into dialysis tubing and dialyzed against 3×1 L for 48 h. Thesolution was then concentrated by lyophilization to 0.2 mL.

[0477] C) Synthesis of L-cystine-1,4-bis(3-aminopropyl)piperazinecopolymer. To a solution of N,N′-Bis(t-BOC)-L-cystine (85 mg, 0.15 mmol)in ethyl acetate (20 mL) was added N,N′-dicyclohexylcarbodiimide (108mg, 0.5 mmol) and N-hydroxysuccinimide (60 mg, 0.5 mmol). After 2 hr,the solution was filtered through a cotton plug and1,4-bis(3-aminopropyl)piperazine (54 mL, 0.25 mmol) was added. Thereaction was allowed to stir at room temperature for 16 h. The ethylacetate was then removed by rotary evaporation and the resulting solidwas dissolved in trifluoroacetic acid (9.5 mL), water (0.5 mL) andtriisopropylsilane (0.5 mL). After 2 h, the trifluoroacetic acid wasremoved by rotary evaporation and the aqueous solution was dialyzed in a15,000 MW cutoff tubing against water (2×2 l) for 24 h. The solution wasthen removed from dialysis tubing, filtered through 5 μM nylon syringefilter and then dried by lyophilization to yield 30 mg of polymer.

[0478] D) Synthesis of 5,5′-Dithiobis(2-nitrobenzoicacid)-1,4-Bis(3-aminopropyl)piperazine Copolymer.1,4-Bis(3-aminopropyl)piperazine (10 mL, 0.050 mmol, Aldrich ChemicalCompany) was taken up in 1.0 mL methanol and HCl (2 mL, 1 M in Et2O,Aldrich Chemical Company) was added. Et2O was added and the resultingHCl salt was collected by filtration. The salt was taken up in 1 mL DMFand 5,5′-dithiobis[succinimidyl(2-nitrobenzoate)] (30 mg, 0.050 mmol)was added. The resulting solution was heated to 80° C. anddiisopropylethylamine (35 mL, 0.20 mmol, Aldrich Chemical Company) wasadded by drops. After 16 hr. the solution was cooled, diluted with 3 mLH2O, and dialyzed in 12,000-14,000 MW cutoff tubing against water (2×2L) for 24 h. The solution was then removed from dialysis tubing anddried by lyophilization to yield 23 mg (82%) of5,5′-dithiobis(2-nitrobenzoic acid)-1,4-bis(3-aminopropyl)piperazinecopolymer.

[0479] E) Synthesis of polypropylacrylic acid. To a solution ofdiethylpropylmalonate (2 g, 10 mmol) in 50 mL ethanol was addedpotassium hydroxide (0.55 g, 1 eq) and the mixture was stirred at roomtemperature for 16 hours. The ethanol was then removed by rotaryevaporation. The reaction mixture was partitioned between 50 mL ethylacetate and 50 mL of water. The aqueous solution was isolated, andacidified with hydrochloric acid. The solution was again partitionedbetween ethyl acetate and water. The ethyl acetate layer was isolated,dried with sodium sulfate, and concentrated to yield a clear oil. Tothis oil was added 20 mL of pyridine, paraformaldehyde (0.3 g, 10 mmol),and 1 mL piperidine. The mixture was refluxed at 130° C. until theevolution of gas was observed, ca. 2 hours. The ester product was thendissolved into 100 mL ethyl ether, which was washed with 100 mL 1Mhydrochloric acid, 100 mL water, and 100 mL saturated sodiumbicarbonate. The ether layer was isolated, dried with magnesium sulfate,and concentrated by rotary evaporation to yield a yellow oil. The esterwas then hydrolyzed by dissolving in 50 mL ethanol with addition ofpotassium hydroxide (0.55 gm, 10 mmol). After 16 hours, the reactionmixture was acidified by the addition of hydrochloric acid. Thepropylacrylic acid was purified by vacuum distillation (0.9 g, 80%yield), boiling point of product is 60° C. at 1 torr. The propylacrylicacid was polymerized by addition of 1 mole percent ofazobisisobutyonitrile and heating to 60° C. for 16 hours. Thepolypropylacrylic acid was isolated by precipitation with ethyl ether.

[0480] F) Synthesis of poly N-terminal acryloyl 6-aminohexanoyl-SEQ IDNO: 10-CO₂ (pAcKL₃). A solution of AcKL3 (20 mg, 7.7 μmol) in 0.5 mL of6 M guanidinium hydrochloride, 2 mM EDTA, and 0.5 M Tris pH 8.3 wasdegassed by placing under a 2 torr vacuum for 5 minutes. Polymerizationof the acrylamide was initiated by the addition of ammonium persulfate(35 μg, 0.02 eq.) and N,N,N,N-tetramethylethylenediamine (1 μL). Thepolymerization was allowed to proceed overnight. The solution was thenplaced into dialysis tubing (12,000 molecular weight cutoff) anddialyzed against 3×2 L over 48 hours. The amount of polymerized peptide(6 mg, 30% yield) was determined by measuring the absorbance of thetryptophan residue at 280 nm, using an extinction coefficient of 5690cm⁻¹M⁻¹ (Gill, S. C. and von Hippel, P. H. Analytical Biochemistry(1989) 182, 319-326)

Example 4

[0481] Kinetic Analysis

[0482] A) Kinetics of conversion of dimethyl maleamic modifiedpoly-L-lysine to poly-L-lysine. Dimethyl maleamic modified poly-L-lysine(10 mg/mL) was incubated in 10 mM sodium acetate buffer pH 5. At varioustimes, aliquots (10 μg) were removed and added to 0.5 mL of 100 mM boraxsolution containing 0.4 mM trinitrobenzenesulfonate. A half an hourlater, the absorbance of the solution at 420 nm was measured. Todetermine the concentration of amines at each time point, the extinctioncoefficient was determine for the product of trinitrobenzenesulfonateand poly-L-lysine. Using this extinction coefficient we were able tocalculate the amount of amines and maleamic groups at each time point. Aplot of ln (A_(t)/A₀) as a function of time was a straight line whoseslope is the negative of the rate constant for the conversion ofmaleamic acid to amine and anhydride, where A_(t) is the concentrationof maleamic acid at a time t and A₀ is the initial concentration ofmaleamic acid. For two separate experiments we calculated rate constantsof 0.066 sec⁻¹ and 0.157 sec⁻¹ which correspond to half lives of roughly10 and 4 minutes respectively.

[0483] B) Kinetics of conversion of dimethylmaleamic modified KL₃(DM-KL₃) to KL₃. Dimethyl maleamic modified KL₃ (0.1 mg/mL) wasincubated in 40 mM sodium acetate buffer pH 5 and 1 mMcetyltrimetylammonium bromide. At various times, aliquots (10 μg) wereremoved and added to 0.05 mL of 1 M borax solution containing 4 mMtrinitrobenzenesulfonate. A half an hour later, the absorbance of thesolution at 420 nm was measured. To determine the concentration ofamines at each time point, the extinction coefficient was determine forthe product of trinitrobenzenesulfonate and poly-L-lysine. Using thisextinction coefficient we were able to calculate the amount of aminesand maleamic groups at each time point. A plot of ln (A_(t)/A₀) as afunction of time was a straight line whose slope is the negative of therate constant for the conversion of maleamic acid to amine andanhydride, where A_(t) is the concentration of maleamic acid at a time tand A₀ is the intial concentration of maleamic acid. We calculated arate constant of 0.087 sec⁻¹ that corresponds to a half-life of roughly8 minutes.

[0484] C) Kinetics of hydrolysis of glycolic acid ethoxylate(4 units)4-tert-buty-1,4-cyclohexadiene. Glycolic acid ethoxylate(4 units)4-tert-buty-1,4-cyclohexadiene (1 mg) was dissolved in placed into 1 mLof 15 mM sodium acetate pH 5 buffer. The absorbance of the solution at225 nm, which is the wavelength at which enol ethers absorb (Kresge, A.J.; Sagatys, D. S.; Chen, H. L. J. Am. Chem. Soc. 1977, 99, 7228) wasmeasured over time. A fit of the decrease of absorbance as a function oftime by an exponential decay function had a rate constant of 0.0159min⁻¹, which corresponds to a half-life of 40 minutes.

[0485] D) Kinetics of hydrolysis ofpoly(oxy-1-para-aceticphenoxymethylethylene-co-oxy-1-methylethylene).Poly(oxy-1-para-aceticphenoxymethylethylene-co-oxy-1-methylethylene)(0.16 mg/mL) was placed into 1 mL of 5 mM sodium acetate buffer pH 5.The absorbance of the solution at 225 nm was measured as a function oftime. The amount of time it took for the absorbance to decrease half ofmaximum was 37 minutes, i.e. the half-life of hydrolysis is 37 minutes.

[0486] E) Particle Formation ofpoly(oxy-1-para-aceticphenoxymethylethylene-co-oxy-1-methylethylene) asa Function of Acidification and Time. To a solution (0.5 mL) of 5 mMHEPES pH 8 was addedpoly(oxy-1-para-aceticphenoxymethylethylene-co-oxy-1-methylethylene) (54μg/mL) which had been incubated for various times in the presence of 1mM acetic acid (pH4-5), followed by the addition of polyallylamine. Theintensity of the scattered light and the size of the particle weremeasured (using a Brookhaven ZetaPlus Particle Sizer) as a function ofthe amount of time the polymer was incubated under acidic conditions.Scattered light intensity Time at pH 4-5 (minutes) Size (nm) (kilocountsper second) 0 231 390 1 195 474 2 208 460 5 224 450 15  124  92 39  132250

[0487] F) Kinetics of Cleavage of Ketal, Synthesis of MicrospheresContaining Acid Labile Ketal Moieties:

[0488] F1) Esterification of Carboxylic Acid Modified Microspheres withDi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene. To a suspensionof carboxylic acid modified microspheres (1000 μL, 2% solids, MolecularProbes) in H₂O (500 μL) was added1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (7.0 mg, 36μmol, Aldrich Chemical Company), followed bydi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (23 mg, 73μmol), and the suspension was stirred at room temperature. After 16 hrs,the microspheres were removed by centrifugation. The supernatant wasremoved and the pellet was resuspended in 1.5 mL H₂O to wash. Themicrospheres were washed an additional 2×1.5 mL H₂O and suspended in 1mL H₂O.

[0489] F2) Aldehyde Derivatization of Esterified Carboxylic AcidModified Microspheres withDi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene. To a solutionof succinic semialdehyde (3.7 mg, 36 μmol, Aldrich Chemical Company) inH₂O was added 1-(3-dimethylaminopropyl)-3-ethylcarbodiimidehydrochloride (8.7 mg, 46 μmol, Aldrich Chemical Company) followed byN-hydroxysuccinimide (5.3 mg, 46 μmol, Aldrich Chemical Company). Thesolution was stirred for 20 min at which time carboxylic acid modifiedmicrospheres esterified withdi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene (500 μL) wereadded. After 16 hrs, the microspheres were removed by centrifugation.The supernatant was removed and the pellet was resuspended in 1 mL H₂Oto wash. The microspheres were washed an additional 2×1 mL H₂O andsuspended in 1 mL H₂O. The aldehyde content of the microspheres wasdetermined on a 50 μL sample of the suspension with2,4-dinitrophenylhydrazine and NaBH₃CN. The absorbance measured at 349nm and fitted against a standard curve indicated 18 μmol of aldehydepresent in the reaction sample.

[0490] Attachment of Membrane Active Peptide to Acid Labile Moieties andLability Studies of these Systems:

[0491] F3) Attachment of a Peptide (Melittin) to the Aldehyde Derivedfrom Carboxylic Acid Modified Microspheres Esterified withDi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene. To 100 μL ofthe aldehyde derivatized microshpere suspension was added 400 μL H₂O andmelittin (1 mg, 0.4 μmol, Mirus Corporation). After 12 hrs, NaBH₃CN (0.6mg, 9 μmol, Aldrich Chemical Company) was added. After 1 hr, thesuspension was centrifugated to pellatize the microspheres. Thesupernatant was removed and the pellet was resuspended in 1 mL H₂O towash. The microspheres were washed an additional 3×1 mL H₂O andsuspended in 1 mL H₂O. The last wash indicated the presence of activepeptide based on red blood cell lysis activity. The sample was washed1×25 mM HEPES, and 1×H₂O. The final wash was free of peptide based onred blood cell lysis assay.

[0492] F4) Blood Lysis Experiment on Melittin Conjugated to Microspheresvia the Di-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene. Themicrospheres were taken up in H₂O (500 μL) and partitioned into five 100μL samples. Four of the samples were diluted to 1000 μL with sodiumphosphate buffer (100 mM) at pH 7.5, 6.0, 5.5, and 5.0. Samples wereheld at 37° C., spun down, and 150 μL aliquots taken at 30 min, 60 min,90 min, and 16 hrs. A portion of each sample (100 μL) was diluted withsodium phosphate buffer (400 μL, pH 7.5) and added to red blood cells(100 μL, pH 7.5). Red blood cell lysis was measured after 10 min bymeasuring the absorbance at 541 nm.

[0493] A control sample was also measured in which 100% of the red bloodcells had been lysed with melittin alone. Sample A₅₄₁ Blood 0.026 100%lysis 1.881 30 min pH 7.5 0.026 30 min pH 6.0 0.326 30 min pH 5.5 0.60930 min pH 5.0 0.659 60 min pH 7.5 0.027 60 min pH 6.0 0.212 60 min pH5.5 0.526 60 min pH 5.0 0.730 90 min pH 7.5 0.036 90 min pH 6.0 0.390 90min pH 5.5 0.640 90 min pH 5.0 0.892 16 hrs pH 7.5 0.065 16 hrs pH 6.00.354 16 hrs pH 5.5 0.796 16 hrs pH 5.0 1.163

[0494] The fifth 100 μL sample was further divided into 25 μL samples,three of which were diluted to 250 μL with sodium phosphate buffer (100mM) at pH 7.5, 6.0, and 5.0. The samples were held at 37° C. for 30 min,spun down and the supernatant removed, and resuspended in 2.5 M NaClsolution (50 μL) and mixed. After 10 min the microspheres were spun downand the supernatant removed. The samples were added to red blood cells(500 μL, 100 mM) and the absorbance was measured at 541 nm. Sample A₅₄₁Blood (NaCl wash) 0.041 pH 7.5 0.053 pH 7.5 (NaCl wash) 0.087 pH 6.00.213 pH 6.0 (NaCl wash) 0.162 pH 5.0 0.685 pH 5.0 (NaCl wash) 0.101

[0495] The results indicate that under acidic conditions, the modifiedpeptide is released from the microsphere and is available to interactwith the cell membrane as indicated by the red blood cell lysis. Theresults indicate that the modified peptide is not released at pH 7.5.Additionally, the lysis activity results indicate the release ofmodified peptide is rapid at all acidic pH levels tested (t<30 min) withslow continual release thereafter, and that more modified peptide isreleased at lower pH (larger red blood cell lysis). The results alsoindicate that more modified peptide is released upon washing themicrosphere with a salt solution.

[0496] F5) Attachment of a Peptide (Melittin) to the Aldehyde Derivedfrom Poly-Glutamic Acid Partially Esterified withDi-(2-methyl-4-hydroxymethyl-1,3-dioxolane)-1,4-benzene. To a solutionof the aldehyde-poly-glutamic acid compound (1.0 mg, 7.7 μmol) in water(200 μL) was added melittin (4.0 mg, 1.4 μmol) and the reaction mixturewas stirred at room temperature. After 12 hrs the reaction mixture wasdivided into two equal portions. One sample (100 μL) was dialyzedagainst 1% ethanol in water (2×1L, 12,000-14,000 MWCO) and testedutilizing a theoretical yield of 1.7 mg. To the second portion (100 μL)was added sodium cyanoborohydride (1.0 mg, 16 μmol, Aldrich ChemicalCompany). The solution was stirred at room temperature for 1 hr and thendialyzed against water (2×1L, 12,000-14,000 MWCO). The resultingmaterial was utilized assuming a theoretical yield of 1.7 mg ofconjugate.

[0497] Lability of Polymers Containing Acid Labile Moieties:

[0498] F6) Particle Sizing and Acid Lability of Poly-L-Lysine/Ketal Acidof Polyvinylphenyl Ketone and Glycerol Ketal Complexes. Particle sizing(Brookhaven Instruments Corporation, ZetaPlus Particle Sizer, 190, 532nm) indicated an effective diameter of 172 nm (40 μg) for the ketalacid. Addition of acetic acid to a pH of 5 followed by particle sizingindicated a increase in particle size to 84000 nm. A poly-L-lysine/ketalacid (40 μg, 1:3 charge ratio) sample indicated a particle size of 142nm. Addition of acetic acid (5 μL, 6 N) followed by mixing and particlesizing indicated an effective diameter of 1970 nm. This solution washeated at 40° C. Particle sizing (by a Brookhaven ZetaPlus ParticleSizer) indicated an effective diameter of 74000 nm and a decrease inparticle counts.

[0499] Results: The particle sizer data indicates the loss of particlesupon the addition of acetic acid to the mixture.

[0500] F7) Particle Sizing and Acid Lability of Poly-L-Lysine/Ketal fromPolyvinyl Alcohol and 4-Acetylbutyric Acid Complexes. Particle sizing(Brookhaven Instruments Coporation, ZetaPlus Particle Sizer, 190, 532nm) indicated an effective diameter of 280 nm (743 kcps) forpoly-L-lysine/ketal from polyvinyl alcohol and 4-acetylbutyric acidcomplexes (1:3 charge ratio). A poly-L-lysine sample indicated noparticle formation. Similarly, a ketal from polyvinyl alcohol and4-acetylbutyric acid sample indicated no particle formation. Acetic acidwas added to the poly-L-lysine/ketal from polyvinyl alcohol and4-acetylbutyric acid complex to a pH of 4.5. Particle sizing (by aBrookhaven ZetaPlus Particle Sizer) indicated particles of 100 nm, butat a low count rate (9.2 kcps). Results: The particle size dataindicates the loss of particles upon the addition of acetic acid to themixture.

[0501] F8) Size Exclusion Chromatography and Acid Lability of MC228.MC208 (1.5 mg) was taken up in 50 mM HEPES (0.3 mL, pH 8.5) and passedthrough a Sephadex G50 column (8 cm column, 50 mM HEPES (pH 8.5) eluent)and 0.5 mL fractions were collected. The absorbance of the fractions wasdetermined at 300 nm. Two additional samples (1.5 mg) were prepared in50 mM Citrate buffer at pH 2 and pH 5 (0.3 mL) and allowed to sit a roomtemperature for 45 min prior to running on the Sephadex G50 column (8 cmcolumn, 50 mM HEPES (pH 8.5) eluent). The absorbance of the fractionswas determined at 300 nm. Fraction number pH 8.5 pH 5 pH 2 1 0.018 0.0400.022 2 0.024 0.019 0.013 3 0.019 0.015 0.008 4 0.028 0.118 0.024 50.287 0.527 0.293 6 1.091 0.693 0.604 7 0.976 0.818 0.715 8 0.888 1.0710.895 9 0.907 1.178 1.082 10 0.944 1.289 1.298 11 0.972 1.296 1.423 120.941 1.212 1.326 13 0.913 0.924 1.140 14 0.764 0.640 1.012 15 0.5890.457 0.841 16 0.415 0.264 0.655

[0502] Results: The column demonstrates that upon incubating the sampleunder acidic conditions, the molecular weight of the polymer isdecreased indicating the polymer is labile under acidic conditions.

[0503] F9) Acid Lability of MC208. A sample of MC208 indimethylformamide (20 μL) was divided into four equal samples. To eachsample was added citrate buffer (100 μL, pH 4) and the resulting samples(final pH of 5) were incubated at 37° C. for 2, 4, 8, and 24 hrs. Thesamples were then analyzed by thin layer chromatography against a samplenot exposed to acidic conditions.

[0504] The results indicated increasing amounts of higher Rf materialwith increasing time, indicated degredation of the polymer.

[0505] F10) Particle Sizing and Acid Lability of pDNA (pCI Luc)/MC208Complexes. Particle sizing (Brookhaven Instruments Coporation, ZetaPlusParticle Sizer, 190, 532 nm) indicated an effective diameter of 293 nm(687 kcps) for pDNA (25 μg pDNA)/di-(2-methyl-4-hydroxymethyl(succinicsemialdehyde ester)-1,3-dioxolane)-1,4-benzene:1,4-bis(3-aminopropyl)-piperazine copolymer complexes (1:3 chargeratio). HCl was added to the complex to approximately pH 5 and theparticle size was measured. The reading indicated particles with aneffective diameter of 11349 nm (120 kcps).

[0506] Results: The particle size data indicates MC208 compacts pDNAinto small particles. The results also indicate the loss of particlesupon the addition of HCl to the mixture by floculation.

[0507] G) Kinetics of Cleavage of Imine. Particle Sizing and AcidLability of pDNA (pCl Luc)/1,4-Bis(3-aminopropyl)piperazine GlutaricDialdehyde Copolymer Complexes. To 50 μg pDNA in 2 mL HEPES (25 mM, pH7.8) was added 135 μg 1,4-bis(3-aminopropyl)piperazine glutaricdialdehyde copolymer. Particle sizing (Brookhaven InstrumentsCoporation, ZetaPlus Particle Sizer, 190, 532 nm) indicated an effectivediameter of 110 nm for the complex. A 50 μg pDNA in 2 mL HEPES (25 mM,pH 7.8) sample indicated no particle formation. Similarly, a 135 μg1,4-bis(3-aminopropyl)piperazine glutaric dialdehyde copolymer in 2 mLHEPES (25 mM, pH 7.8) sample indicated no particle formation. Aceticacid was added to the pDNA (pCI Luc)/1,4-bis(3-aminopropyl)piperazineglutaric dialdehyde copolymer complex to a pH of 4.5. Particle sizingindicated particles of 2888 nm, and aggregation was observed.

[0508] Results: 1,4-Bis(3-aminopropyl)piperazine-glutaric dialdehydecopolymer condenses pDNA, forming small particles. Upon acidification,the particle size increases, and aggregation occurs, indicating cleavageof the polymeric imine.

Example 5

[0509] Hemolysis Assay

[0510] A) Lysis of Erythrocytes by the peptides Melittin and KL3 andtheir dimethylmaleamic acid derivatives as a function of pH. Themembrane-disruptive activity of the peptide melittin and subsequentblocking of activity by anionic polymers was measured using a red bloodcell (RBC) hemolysis assay. RBCs were harvested by centrifuging wholeblood for 4 min. They were washed three times with 100 mM dibasic sodiumphosphate at the desired pH, and resuspended in the same buffer to yieldthe initial volume. They were diluted 10 times in the same buffer, and200 uL of this suspension was used for each tube. This yields10{circumflex over ( )}8 RBCs per tube. Each tube contained 800 uL ofbuffer, 200 uL of the RBC suspension, and the peptide with or withoutpolymer. Each sample was then repeated to verify reproducibility. Thetubes were incubated for 30 minutes in a 37° C. water bath. They werespun for 5 min at full speed in the microcentifuge. Lysis was determinedby measuring the absorbance of the supernatant at 541 nm, reflecting theamount of hemoglobin that had been released into the supernatant.Percent hemolysis was calculated assuming 100% lysis to be measured bythe hemoglobin released by the red blood cells in water; controls ofRBCs in buffer with no peptide were also run. Percent Hemolysis PeptidepH 5.4 pH 7.5 Unmodified Peptides KL₃ 86, 77, 86 54, 77, 54 Melittin 8592 Dimethylmaleamic Derivatives KL₃ 30, 55, 26 8, 3, 2 Melittin 100 1Succinyl Derivatives KL₃ 2, 2, 2 1, 1, 2 Melittin 5 2

[0511] B) Lysis of Erythrocytes by Poly Propacrylic Acid and subsequentblocking of activity by cationic polymers with reversible blocking ofactivity with cleavable disulfide cations in the presence ofGlutathione. The pH-dependent membrane-disruptive activity of the PPAAcand subsequent blocking of activity by cationic polymers was measuredusing a red blood cell (RBC) hemolysis assay. RBCs were harvested bycentrifuging whole blood for 4 min. They were washed three times with100 mM dibasic sodium phosphate at the desired pH, and resuspended inthe same buffer to yield the initial volume. They were diluted 10 timesin the same buffer, and 200 L of this suspension was used for each tube.This yields 10{circumflex over ( )}8 RBCs per tube. Each tube contained800 L of buffer, 200 L of the RBC suspension, and the polymer. Eachsample was done in triplicate, and was then repeated to verifyreproducibility. The tubes were incubated for an hour and a half in a37° C. water bath. They were spun for 5 min at full speed in themicrocentifuge. Lysis was determined by measuring the absorbance of thesupernatant at 541 nm, reflecting the amount of hemoglobin which hadbeen released into the supernatant. Percent hemolysis was calculatedassuming 100% lysis to be measured by the hemoglobin released by the redblood cells in water; controls of RBCs in buffer with no polymer werealso run. Results at pH 6.0: Mock: 3% PPAAc: 98% PPAAc + p-L-Lysine 3%PPAAc + p-L-Lysine w/1 mM Glutathione 2% PPAAc +5,5′-Dithiobis(2-nitrobenzoic acid)- 12%1,4-Bis(3-aminopropyl)piperazine Copolymer PPAAc +5,5′-Dithiobis(2-nitrobenzoic acid)- 98%1,4-Bis(3-aminopropyl)piperazine Copolymer w/1 mM Glutathione PPAAc +L-cystine − 1,4-bis(3-aminopropyl)piperazine copolymer 2% PPAAc +L-cystine − 1,4-bis(3-aminopropyl)piperazine copolymer 20% w/1 mMGlutathione

[0512] C) Lysis of Erythrocytes by the peptide Melittin or KL3 andsubsequent blocking of activity by anionic polymers or modification withdimethylmaleic anhydride. The membrane-disruptive activity of thepeptide melittin and subsequent blocking of activity by anionic polymerswas measured using a red blood cell (RBC) hemolysis assay. RBCs wereharvested by centrifuging whole blood for 4 min. They were washed threetimes with 100 mM dibasic sodium phosphate at the desired pH, andresuspended in the same buffer to yield the initial volume. They werediluted 10 times in the same buffer, and 200 uL of this suspension wasused for each tube. This yields 10{circumflex over ( )}8 RBCs per tube.Each tube contained 800 uL of buffer, 200 uL of the RBC suspension, andthe peptide with or without polymer. Each sample was then repeated toverify reproducibility. The tubes were incubated for 30 minutes in a 37°C. water bath. They were spun for 5 min at full speed in themicrocentifuge. Lysis was determined by measuring the absorbance of thesupernatant at 541 nm, reflecting the amount of hemoglobin that had beenreleased into the supernatant. Percent hemolysis was calculated assuming100% lysis to be measured by the hemoglobin released by the red bloodcells in water; controls of RBCs in buffer with no peptide were alsorun. Results at pH 7.5: Mock: 1% Melittin 100% Melittin + pAcrylic Acid9% DM-Melittin 1% DM-Melittin post incubation at pH 4 30 seconds 100%KL3 86% DM-KL3 4% DM-KL3 post incubation at pH 5.4 30 seconds 85%

Example 6

[0513] Endosome Lysis

[0514] Endosome Disruption Assay: with Dimethylmaleamic-modifiedmelittin. HeLa cells were plated in 6-well tissue culture dishescontaining microscope slide coverslips and grown in Delbecco's ModifiedEagle's Medium (DMEM) +10% fetal calf serum +penn/strep for 24-48 hoursuntil 30-60% confluent. Growth media was aspirated and 1 ml pre-heated(37° C.) serum-free DMEM +2 mg/ml fluorescein isothiocyanate (FITC)labeled dextran(10 kDa)±50 μg DM-melittin or 50 μg melittin was added tothe cells and incubated at 37° C. in a humidified CO₂ incubator. After25 min, media containing FITC-dextran+melittin was removed, the cellswere washed twice with 1 ml 37° C. DMEM lacking FITC-dextran andmelittin, and cells were incubated for an additional 35 min at 37° C. in1 ml fresh DMEM. In order to assess possible cell lysis caused bymelittin, propidium iodide was added for the final 5 min of incubation.Propidium iodide is impermeable to the cell plasma membrane and thusdoes not stain live cells. However, if the plasma membrane has beendamaged, propidium iodide enters the cell where it will brightly stainthe nucleus. To process slides for analysis, cells were washed 3 timeswith cold phosphate buffered saline (PBS), fixed in PBS+4% formaldehydefor 20-30 min at 4° C., and washed again 3 times with cold PBS. Excessliquid was drained from coverslips which were then mounted onto glassslides. Fluorescence was then analyzed on a Zeiss LSM510 confocalmicroscope. FITC was excited by a 488 nm argon laser and fluorescenceemission was detected by a long pass 505 nm filter. FITC-dextran thathad been internalized but not released from internal vesicles/endosomesappeared as a punctate cytoplasmic signal. In the presence ofDM-melittin, a loss of punctate cytoplasmic signal was observed with aconcomitant appearance of a diffuse cytoplasmic signal, indicative ofrelease of dextran from endosomes. For cells incubated with unmodifiedmelittin near 100% cell death was observed as determined by propidiumiodide staining of nuclei and loss of cells from the sample.

Example 7

[0515] In Vivo Circulation Studies. General procedure for the reactionof poly-L-Lysine compacted DNA particles polyethylene glycol methylether 2-propionic-3-methylmaleate (CDM-PEG). Plasmid DNA (200 μg/ml) in290 mM Glucose/5 mM Hepes pH8 was compacted with poly-L-Lysine (mw:52,000) (144 μg/ml). This particle is then reacted with 0.5, 1, 2 or5-fold weight excess of CDM-PEG to amines on the poly-L-lysine.

[0516] Effect of CDM-PEG modified poly-L-lysine:DNA particles in vivo.Plasmid DNA labeled with Cy3 Label IT(Mirus Corporation, Madison, Wis.)was compacted into a particle with a 1.2 fold charge excess ofpoly-L-lysine (mw: 52,000). The particles were then reacted with eithera non-reactive Polyethylene Glycol (mw: 5000) or with amine-reactiveCDM-PEG at a 0.5 molar equivalent to amines on the poly-L-lysine. 50 μgaliquots of DNA were injected into the tail vein of male ICR mice ofapproximately 20 grams in weight. Blood was taken at one hour and thesmears were inspected for Cy3 fluorescence still in circulation. Theanimals were then sacrificed and the liver, lung, kidney and spleen wereharvested and snap frozen for cryosectioning and the resulting sliceswere inspected for Cy3 fluorescence.

[0517] Results:

[0518] The animal injected with the fluorescent particles treated withnon-reactive Polyethylene Glycol showed no fluorescence in circulationin the blood at one hour and very little fluorescence in the liver,kidney or spleen, leaving the significant portion of fluorescence in thelung. The animal injected with the fluorescent particles treated withCDM-PEG showed a high level of fluorescence still in circulation in theblood at one hour and also had a high level of fluorescence evenlyspread throughout the liver, some spread in the kidney and spleen, withlittle fluorescence in the lung.

[0519] Various Compounds which may be Utilized in the System Provided:

[0520] Various modifications and variations of the described method andsystem of the invention will be apparent to those skilled in the artwithout departing from the scope and spirit of the invention. Althoughthe invention has been described in connection with specific preferredembodiments, it should be understood that the invention as claimedshould not be unduly limited to such specific embodiments. Indeed,various modifications of the described modes for carrying out theinvention which are obvious to those skilled in cell biology, chemistry,molecular biology, biochemistry or related fields are intended to bewithin the scope of the following claims.

1 11 1 14 PRT SV40 1 Cys Gly Tyr Gly Pro Lys Lys Lys Arg Lys Val Gly GlyCys 1 5 10 2 13 PRT SV40 2 Cys Gly Tyr Gly Pro Lys Lys Lys Arg Lys ValGly Gly 1 5 10 3 39 PRT SV40 3 Cys Lys Lys Lys Ser Ser Ser Asp Asp GluAla Thr Ala Asp Ser Gln 1 5 10 15 His Ser Thr Pro Pro Lys Lys Lys ArgLys Val Glu Asp Pro Lys Asp 20 25 30 Phe Pro Ser Glu Leu Leu Ser 35 4 37PRT SV40 4 Cys Lys Lys Lys Trp Asp Asp Glu Ala Thr Ala Asp Ser Gln HisSer 1 5 10 15 Thr Pro Pro Lys Lys Lys Arg Lys Val Glu Asp Pro Lys AspPhe Pro 20 25 30 Ser Glu Leu Leu Ser 35 5 31 PRT SV40 5 Cys Tyr Asn AspPhe Gly Asn Tyr Asn Asn Gln Ser Ser Asn Phe Gly 1 5 10 15 Pro Met LysGln Gly Asn Phe Gly Gly Arg Ser Ser Gly Pro Tyr 20 25 30 6 10 PRT SV40 6Cys Lys Arg Gly Pro Lys Arg Pro Arg Pro 1 5 10 7 22 PRT SV40 7 Cys LysLys Ala Val Lys Arg Pro Ala Ala Thr Lys Lys Ala Gly Gln 1 5 10 15 AlaLys Lys Lys Lys Leu 20 8 14 PRT SV40 8 Cys Lys Lys Lys Gly Pro Ala AlaLys Arg Val Lys Leu Asp 1 5 10 9 4 PRT ER retaining signal 9 Lys Asp GluLeu 1 10 21 PRT KL3 10 Lys Leu Leu Lys Leu Leu Leu Lys Leu Trp Leu LysLeu Leu Lys Leu 1 5 10 15 Leu Leu Lys Leu Leu 20 11 8 PRT MC151 11 GluGlu Glu Glu Glu Glu Glu Glu 1 5

We claim:
 1. A process for delivering a nucleic acid to a cell,comprising: a) attaching a labile linkage to a membrane-active compound;b) adding the membrane-active compound to a solution containing thenucleic acid; c) introducing the membrane-active compound and nucleicacid to a cell; and, d) transfecting the cell.
 2. The process of claim 1wherein the labile linkage is selected from the group consisting ofpH-labile, very pH-labile and extremely pH-labile.
 3. The process ofclaim 1 wherein the labile linkage is selected from the group consistingof disulfide, acetal, ketal, enol ether, enol ester, amide, imine,imminium, enamine, silyl ether, silazane, and silyl enol ether bonds. 4.The process of claim 2 wherein the labile linkage is selected from thegroup consisting of diols, diazo, ester, sulfone, and silicon-carbonbonds.
 5. The process of claim 1 wherein the membrane active compoundconsists of a polymer.
 6. The process of claim 5 wherein the polymerconsists of a peptide.
 7. The process of claim 6 wherein the peptideconsists of melittin.
 8. The process of claim 6 wherein the peptideconsists of KL3.
 9. The process of claim 6 wherein the peptide consistsof pardaxin.
 10. The process of claim 1 further comprising a polymer inthe solution.
 11. The process of claim 10 wherein the polymer isattached to the membrane-active compound by the labile linkage.
 12. Theprocess of claim 11 wherein the polymer inhibits the membrane-activecompound.
 13. A process for delivering a nucleic acid to a cell,comprising: a) attaching a labile linkage to a polymer for linking to amolecule; b) adding the polymer to a solution containing the nucleicacid; c) introducing the polymer and nucleic acid to a cell; and, d)transfecting the cell.
 14. The process of claim 13 wherein the labilelinkage is selected from the group consisting of pH-labile, verypH-labile and extremely pH-labile.
 15. The process of claim 13 whereinthe labile linkage is selected from the group consisting of disulfide,acetal, ketal, enol ether, enol ester, amide, imine, imminium, enamine,silazane, silyl ether, and silyl enol ether bonds.
 16. The process ofclaim 14 wherein the labile linkage is selected from the groupconsisting of diols, diazo, ester, sulfone, and silicon-carbon bonds.17. The process of claim 13 further comprising a labile linkage betweena membrane active compound and the polymer.
 18. The process of claim 17wherein the polymer consists of a peptide.
 19. The process of claim 18wherein the peptide consists of melittin.
 20. The process of claim 18wherein the peptide consists of KL3.
 21. The process of claim 18 whereinthe peptide consists of pardaxin.
 22. The process of claim 13 furthercomprising a membrane-active compound in the solution.
 23. The processof claim 22 wherein the polymer is attached to the membrane-activecompound by the labile linkage.
 24. A complex for delivering a nucleicacid to a cell, comprising: a) a membrane-active compound; b) a polymer;and, c) the nucleic acid.
 25. The complex of claim 24 wherein themembrane-active compound contains a labile linkage.
 26. The complex ofclaim 24 wherein the polymer contains a labile linkage.
 27. The complexof claim 25 wherein the polymer is attached to the membrane-activecompound by the labile linkage.
 28. The complex of claim 24 wherein thepolymer inhibits the membrane-active compound.
 29. The process of claim24 wherein the labile linkage is selected from the group consisting ofpH-labile, very pH-labile and extremely pH-labile.
 30. The process ofclaim 24 wherein the labile linkage is selected from the groupconsisting of disulfide, acetal, ketal, enol ether, enol ester, amide,imine, imminium, enamine, silyl ether, silazane, and silyl enol etherbonds.
 31. The process of claim 29 wherein the labile linkage isselected from the group consisting of diols, diazo, ester, sulfone, andsilicon-carbon bonds.
 32. A process for delivering nucleic acids to acell, comprising: a) forming a labile linkage between two compounds toform a complex containing nucleic acid; b) delivering the complex to thecell; c) removing the labile linkage; and, d) transfecting the cell. 33.The process of claim 32 wherein the labile linkage is selected from thegroup consisting of pH-labile, very pH-labile and extremely pH-labile.34. The process of claim 33 wherein the compounds are selected from thegroup consisting of polymers, amphipathic compounds, membrane-activecompounds, nucleic acids, lipids, and liposomes.